diff --git a/changelog_unreleased/typescript/17498.md b/changelog_unreleased/typescript/17498.md
new file mode 100644
index 000000000..77db2f5dd
--- /dev/null
+++ b/changelog_unreleased/typescript/17498.md
@@ -0,0 +1,16 @@
+#### Improve new line detect in mapped type (#17498 by @fisker)
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+type A = { readonly
+ [A in B]: T}
+
+// Prettier stable
+type A = {
+  readonly [A in B]: T;
+};
+
+// Prettier main
+type A = { readonly [A in B]: T };
+```
diff --git a/src/language-js/clean.js b/src/language-js/clean.js
index aa209a344..5dd02f7ed 100644
--- a/src/language-js/clean.js
+++ b/src/language-js/clean.js
@@ -190,12 +190,6 @@ function clean(original, cloned) {
     cloned.expression.type = "ChainExpression";
   }
 
-  // `@typescript-eslint/typescript-estree` v8
-  if (original.type === "TSMappedType") {
-    delete cloned.key;
-    delete cloned.constraint;
-  }
-
   // `@typescript-eslint/typescript-estree` v8
   if (original.type === "TSEnumDeclaration") {
     delete cloned.body;
diff --git a/src/language-js/comments/handle-comments.js b/src/language-js/comments/handle-comments.js
index b9a89e671..84ca9f1b9 100644
--- a/src/language-js/comments/handle-comments.js
+++ b/src/language-js/comments/handle-comments.js
@@ -69,6 +69,7 @@ function handleOwnLineComment(context) {
     handleBreakAndContinueStatementComments,
     handleNestedConditionalExpressionComments,
     handleCommentsInDestructuringPattern,
+    handleTSMappedTypeComments,
   ].some((fn) => fn(context));
 }
 
@@ -95,6 +96,7 @@ function handleEndOfLineComment(context) {
     handleSwitchDefaultCaseComments,
     handleLastUnionElementInExpression,
     handleLastBinaryOperatorOperand,
+    handleTSMappedTypeComments,
   ].some((fn) => fn(context));
 }
 
@@ -113,7 +115,6 @@ function handleRemainingComment(context) {
     handleOnlyComments,
     handleCommentAfterArrowParams,
     handleFunctionNameComments,
-    handleTSMappedTypeComments,
     handleBreakAndContinueStatementComments,
     handleTSFunctionTrailingComments,
   ].some((fn) => fn(context));
@@ -906,8 +907,7 @@ function handleIgnoreComments({ comment, enclosingNode, followingNode }) {
   if (
     isPrettierIgnoreComment(comment) &&
     enclosingNode?.type === "TSMappedType" &&
-    followingNode?.type === "TSTypeParameter" &&
-    followingNode.constraint
+    followingNode === enclosingNode.key
   ) {
     enclosingNode.prettierIgnore = true;
     comment.unignore = true;
@@ -915,27 +915,15 @@ function handleIgnoreComments({ comment, enclosingNode, followingNode }) {
   }
 }
 
-function handleTSMappedTypeComments({
-  comment,
-  precedingNode,
-  enclosingNode,
-  followingNode,
-}) {
+function handleTSMappedTypeComments({ comment, precedingNode, enclosingNode }) {
   if (enclosingNode?.type !== "TSMappedType") {
-    return false;
+    return;
   }
 
-  if (followingNode?.type === "TSTypeParameter" && followingNode.name) {
-    addLeadingComment(followingNode.name, comment);
+  if (!precedingNode) {
+    addDanglingComment(enclosingNode, comment);
     return true;
   }
-
-  if (precedingNode?.type === "TSTypeParameter" && precedingNode.constraint) {
-    addTrailingComment(precedingNode.constraint, comment);
-    return true;
-  }
-
-  return false;
 }
 
 function handleSwitchDefaultCaseComments({
diff --git a/src/language-js/parse/postprocess/index.js b/src/language-js/parse/postprocess/index.js
index c9b464a3e..5d28da2f1 100644
--- a/src/language-js/parse/postprocess/index.js
+++ b/src/language-js/parse/postprocess/index.js
@@ -145,14 +145,7 @@ function postprocess(ast, options) {
 
       case "TSTypeParameter":
         // babel-ts
-        if (typeof node.name === "string") {
-          const start = locStart(node);
-          node.name = {
-            type: "Identifier",
-            name: node.name,
-            range: [start, start + node.name.length],
-          };
-        }
+        fixBabelTSTypeParameter(node);
         break;
 
       // For hack-style pipeline
@@ -167,6 +160,19 @@ function postprocess(ast, options) {
           return node.types[0];
         }
         break;
+
+      // Remove this when update `@babel/parser` to v8
+      // https://github.com/typescript-eslint/typescript-eslint/pull/7065
+      case "TSMappedType":
+        if (!node.constraint && !node.key) {
+          const { name: key, constraint } = fixBabelTSTypeParameter(
+            node.typeParameter,
+          );
+          node.constraint = constraint;
+          node.key = key;
+          delete node.typeParameter;
+        }
+        break;
     }
 
     /* c8 ignore next 3 */
@@ -183,6 +189,19 @@ function postprocess(ast, options) {
   return ast;
 }
 
+function fixBabelTSTypeParameter(node) {
+  if (node.type === "TSTypeParameter" && typeof node.name === "string") {
+    const start = locStart(node);
+    node.name = {
+      type: "Identifier",
+      name: node.name,
+      range: [start, start + node.name.length],
+    };
+  }
+
+  return node;
+}
+
 function isUnbalancedLogicalTree(node) {
   return (
     node.type === "LogicalExpression" &&
diff --git a/src/language-js/print/mapped-type.js b/src/language-js/print/mapped-type.js
index d37f43d07..1cfbe4b48 100644
--- a/src/language-js/print/mapped-type.js
+++ b/src/language-js/print/mapped-type.js
@@ -1,5 +1,6 @@
 import {
   group,
+  hardline,
   ifBreak,
   indent,
   line,
@@ -8,6 +9,8 @@ import {
 import { printDanglingComments } from "../../main/comments/print.js";
 import hasNewlineInRange from "../../utils/has-newline-in-range.js";
 import { locStart } from "../loc.js";
+import getTextWithoutComments from "../utils/get-text-without-comments.js";
+import { CommentCheckFlags, hasComment } from "../utils/index.js";
 
 /**
  * @param {string | null} optional
@@ -52,25 +55,44 @@ function printTypeScriptMappedTypeModifier(tokenNode, keyword) {
   return keyword;
 }
 
-function printTypescriptMappedType(path, options, print) {
+function printTypeScriptMappedType(path, options, print) {
   const { node } = path;
   // Break after `{` like `printObject`
-  const shouldBreak =
-    options.objectWrap === "preserve" &&
-    hasNewlineInRange(
-      options.originalText,
-      locStart(node),
-      // Ideally, this should be the next token after `{`, but there is no node starts with it.
-      locStart(node.typeParameter),
+  let shouldBreak = false;
+  if (options.objectWrap === "preserve") {
+    const start = locStart(node);
+    const textAfter = getTextWithoutComments(
+      options,
+      start + 1,
+      locStart(node.key),
     );
+    const nextTokenIndex = start + 1 + textAfter.search(/\S/u);
+    if (hasNewlineInRange(options.originalText, start, nextTokenIndex)) {
+      shouldBreak = true;
+    }
+  }
 
   return group(
     [
       "{",
       indent([
         options.bracketSpacing ? line : softline,
+        hasComment(node, CommentCheckFlags.Dangling)
+          ? group([printDanglingComments(path, options), hardline])
+          : "",
         group([
-          print("typeParameter"),
+          node.readonly
+            ? [
+                printTypeScriptMappedTypeModifier(node.readonly, "readonly"),
+                " ",
+              ]
+            : "",
+          "[",
+          print("key"),
+          " in ",
+          print("constraint"),
+          node.nameType ? [" as ", print("nameType")] : "",
+          "]",
           node.optional
             ? printTypeScriptMappedTypeModifier(node.optional, "?")
             : "",
@@ -79,7 +101,6 @@ function printTypescriptMappedType(path, options, print) {
         ]),
         options.semi ? ifBreak(";") : "",
       ]),
-      printDanglingComments(path, options),
       options.bracketSpacing ? line : softline,
       "}",
     ],
@@ -87,8 +108,4 @@ function printTypescriptMappedType(path, options, print) {
   );
 }
 
-export {
-  printFlowMappedTypeProperty,
-  printTypescriptMappedType,
-  printTypeScriptMappedTypeModifier,
-};
+export { printFlowMappedTypeProperty, printTypeScriptMappedType };
diff --git a/src/language-js/print/type-parameters.js b/src/language-js/print/type-parameters.js
index 5368c07ed..083851c92 100644
--- a/src/language-js/print/type-parameters.js
+++ b/src/language-js/print/type-parameters.js
@@ -20,7 +20,6 @@ import {
   shouldPrintComma,
 } from "../utils/index.js";
 import { isArrowFunctionVariableDeclarator } from "./assignment.js";
-import { printTypeScriptMappedTypeModifier } from "./mapped-type.js";
 import {
   printTypeAnnotationProperty,
   shouldHugType,
@@ -127,7 +126,7 @@ function printDanglingCommentsForInline(path, options) {
 }
 
 function printTypeParameter(path, options, print) {
-  const { node, parent } = path;
+  const { node } = path;
 
   /**
    * @type {Doc[]}
@@ -136,27 +135,6 @@ function printTypeParameter(path, options, print) {
 
   const name = node.type === "TSTypeParameter" ? print("name") : node.name;
 
-  if (parent.type === "TSMappedType") {
-    if (parent.readonly) {
-      parts.push(
-        printTypeScriptMappedTypeModifier(parent.readonly, "readonly"),
-        " ",
-      );
-    }
-    parts.push("[", name);
-    if (node.constraint) {
-      parts.push(" in ", print("constraint"));
-    }
-    if (parent.nameType) {
-      parts.push(
-        " as ",
-        path.callParent(() => print("nameType")),
-      );
-    }
-    parts.push("]");
-    return parts;
-  }
-
   if (node.variance) {
     parts.push(print("variance"));
   }
diff --git a/src/language-js/print/typescript.js b/src/language-js/print/typescript.js
index 1d81ab98f..f849ff49c 100644
--- a/src/language-js/print/typescript.js
+++ b/src/language-js/print/typescript.js
@@ -25,7 +25,7 @@ import {
   shouldGroupFunctionParameters,
 } from "./function-parameters.js";
 import { printInterface } from "./interface.js";
-import { printTypescriptMappedType } from "./mapped-type.js";
+import { printTypeScriptMappedType } from "./mapped-type.js";
 import {
   printDeclareToken,
   printOptionalToken,
@@ -230,7 +230,7 @@ function printTypescript(path, options, print) {
       return [node.operator, " ", print("typeAnnotation")];
 
     case "TSMappedType":
-      return printTypescriptMappedType(path, options, print);
+      return printTypeScriptMappedType(path, options, print);
 
     case "TSMethodSignature": {
       const kind = node.kind && node.kind !== "method" ? `${node.kind} ` : "";
diff --git a/src/language-js/traverse/visitor-keys.evaluate.js b/src/language-js/traverse/visitor-keys.evaluate.js
index 9e6ce9742..0c6907088 100644
--- a/src/language-js/traverse/visitor-keys.evaluate.js
+++ b/src/language-js/traverse/visitor-keys.evaluate.js
@@ -62,11 +62,8 @@ const excludeKeys = {
   ExportNamedDeclaration: ["assertions"],
   ImportDeclaration: ["assertions"],
   ImportExpression: ["attributes"],
+  TSMappedType: ["typeParameter"],
 
-  // `key` and `constraint` added in `@typescript-eslint/typescript-estree` v8
-  // https://github.com/typescript-eslint/typescript-eslint/pull/7065
-  // TODO: Use the new AST properties instead
-  TSMappedType: ["key", "constraint"],
   // `body` added in `@typescript-eslint/typescript-estree` v8
   // https://github.com/typescript-eslint/typescript-eslint/pull/8920
   // TODO: Use the new AST properties instead
diff --git a/tests/format/html/multiparser/ts/__snapshots__/format.test.js.snap b/tests/format/html/multiparser/ts/__snapshots__/format.test.js.snap
index dc8edd9c7..9ccd1d622 100644
--- a/tests/format/html/multiparser/ts/__snapshots__/format.test.js.snap
+++ b/tests/format/html/multiparser/ts/__snapshots__/format.test.js.snap
@@ -32,9 +32,7 @@ printWidth: 80
 <html lang="en">
   <head>
     <script lang="ts">
-      type X = {
-        [K in keyof Y]: Partial<K>;
-      };
+      type X = { [K in keyof Y]: Partial<K> };
 
       class Foo<T> {
         constructor(private foo: keyof Apple) {}
diff --git a/tests/format/typescript/comments/__snapshots__/format.test.js.snap b/tests/format/typescript/comments/__snapshots__/format.test.js.snap
index e09c788b6..23576ab6f 100644
--- a/tests/format/typescript/comments/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/comments/__snapshots__/format.test.js.snap
@@ -866,6 +866,12 @@ type L = { [l in L /* commentL */]: string }
 
 type M = { [m in M] /* commentG */: string }
 
+// https://github.com/excalidraw/excalidraw/blob/712f2675195ace8d507f563ec4306efe319b3c84/packages/common/src/utility-types.ts#L61-L64
+type MakeBrand<T extends string> = {
+  /** @private using ~ to sort last in intellisense */
+  [K in \`~brand~\${T}\`]: T;
+};
+
 =====================================output=====================================
 type A = {
   // commentA
@@ -873,7 +879,8 @@ type A = {
 };
 
 type B = {
-  /* commentB */ [b in B]: string;
+  /* commentB */
+  [b in B]: string;
 };
 
 type C = {
@@ -908,6 +915,12 @@ type L = { [l in L /* commentL */]: string };
 
 type M = { [m in M /* commentG */]: string };
 
+// https://github.com/excalidraw/excalidraw/blob/712f2675195ace8d507f563ec4306efe319b3c84/packages/common/src/utility-types.ts#L61-L64
+type MakeBrand<T extends string> = {
+  /** @private using ~ to sort last in intellisense */
+  [K in \`~brand~\${T}\`]: T;
+};
+
 ================================================================================
 `;
 
diff --git a/tests/format/typescript/comments/mapped_types.ts b/tests/format/typescript/comments/mapped_types.ts
index e9839c50d..6d058cf0f 100644
--- a/tests/format/typescript/comments/mapped_types.ts
+++ b/tests/format/typescript/comments/mapped_types.ts
@@ -38,3 +38,9 @@ type K = { [k in /* commentK */ K]: string }
 type L = { [l in L /* commentL */]: string }
 
 type M = { [m in M] /* commentG */: string }
+
+// https://github.com/excalidraw/excalidraw/blob/712f2675195ace8d507f563ec4306efe319b3c84/packages/common/src/utility-types.ts#L61-L64
+type MakeBrand<T extends string> = {
+  /** @private using ~ to sort last in intellisense */
+  [K in `~brand~${T}`]: T;
+};
diff --git a/tests/format/typescript/mapped-type/__snapshots__/format.test.js.snap b/tests/format/typescript/mapped-type/__snapshots__/format.test.js.snap
index fe565652c..32308d7d6 100644
--- a/tests/format/typescript/mapped-type/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/mapped-type/__snapshots__/format.test.js.snap
@@ -129,7 +129,8 @@ type Type = {
 
 type Type = {
   // foo
-  /* bar */ readonly [T in number];
+  /* bar */
+  readonly [T in number];
 };
 
 ================================================================================
diff --git a/tests/format/typescript/mapped-type/break-mode/__snapshots__/format.test.js.snap b/tests/format/typescript/mapped-type/break-mode/__snapshots__/format.test.js.snap
index 403d4b605..34b8d2c0d 100644
--- a/tests/format/typescript/mapped-type/break-mode/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/mapped-type/break-mode/__snapshots__/format.test.js.snap
@@ -20,20 +20,72 @@ T}
 type A7 = { readonly [A in B]: T
 }
 
+type B1 = {  [A in B]: T}
+type B2 = {
+ [A in B]: T}
+type B4 = {  [
+A in B]: T}
+
+type C1 = { +readonly [A in B]: T}
+type C2 = {+
+readonly [A in B]: T}
+type C3 = {
++readonly [A in B]: T}
+
+
+type D1 = { -readonly [A in B]: T}
+type D2 = {-
+readonly [A in B]: T}
+type D3 = {
+-readonly [A in B]: T}
+
 =====================================output=====================================
 type A1 = { readonly [A in B]: T };
 type A2 = {
   readonly [A in B]: T;
 };
-type A3 = {
-  readonly [A in B]: T;
-};
-type A4 = {
-  readonly [A in B]: T;
-};
+type A3 = { readonly [A in B]: T };
+type A4 = { readonly [A in B]: T };
 type A5 = { readonly [A in B]: T };
 type A6 = { readonly [A in B]: T };
 type A7 = { readonly [A in B]: T };
 
+type B1 = { [A in B]: T };
+type B2 = {
+  [A in B]: T;
+};
+type B4 = { [A in B]: T };
+
+type C1 = { +readonly [A in B]: T };
+type C2 = { +readonly [A in B]: T };
+type C3 = {
+  +readonly [A in B]: T;
+};
+
+type D1 = { -readonly [A in B]: T };
+type D2 = { -readonly [A in B]: T };
+type D3 = {
+  -readonly [A in B]: T;
+};
+
+================================================================================
+`;
+
+exports[`issue-10571.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+function foo() {
+  return obj as {[K in any]: any;
+    };
+}
+
+=====================================output=====================================
+function foo() {
+  return obj as { [K in any]: any };
+}
+
 ================================================================================
 `;
diff --git a/tests/format/typescript/mapped-type/break-mode/break-mode.ts b/tests/format/typescript/mapped-type/break-mode/break-mode.ts
index 3bada24aa..c071fd190 100644
--- a/tests/format/typescript/mapped-type/break-mode/break-mode.ts
+++ b/tests/format/typescript/mapped-type/break-mode/break-mode.ts
@@ -11,3 +11,22 @@ type A6 = { readonly [A in B]:
 T}
 type A7 = { readonly [A in B]: T
 }
+
+type B1 = {  [A in B]: T}
+type B2 = {
+ [A in B]: T}
+type B4 = {  [
+A in B]: T}
+
+type C1 = { +readonly [A in B]: T}
+type C2 = {+
+readonly [A in B]: T}
+type C3 = {
++readonly [A in B]: T}
+
+
+type D1 = { -readonly [A in B]: T}
+type D2 = {-
+readonly [A in B]: T}
+type D3 = {
+-readonly [A in B]: T}
diff --git a/tests/format/typescript/mapped-type/break-mode/issue-10571.ts b/tests/format/typescript/mapped-type/break-mode/issue-10571.ts
new file mode 100644
index 000000000..a830223d0
--- /dev/null
+++ b/tests/format/typescript/mapped-type/break-mode/issue-10571.ts
@@ -0,0 +1,4 @@
+function foo() {
+  return obj as {[K in any]: any;
+    };
+}
diff --git a/tests/format/typescript/prettier-ignore/__snapshots__/format.test.js.snap b/tests/format/typescript/prettier-ignore/__snapshots__/format.test.js.snap
index 865c74682..574b60950 100644
--- a/tests/format/typescript/prettier-ignore/__snapshots__/format.test.js.snap
+++ b/tests/format/typescript/prettier-ignore/__snapshots__/format.test.js.snap
@@ -146,7 +146,7 @@ type a = {
 };
 
 type a = {
-  [A in B /* prettier-ignore */]: C | D;
+  [A in B]: /* prettier-ignore */ C  |  D;
 };
 
 type a = {
diff --git a/tests/unit/__snapshots__/visitor-keys.js.snap b/tests/unit/__snapshots__/visitor-keys.js.snap
index 702675cd5..f29ea2b9c 100644
--- a/tests/unit/__snapshots__/visitor-keys.js.snap
+++ b/tests/unit/__snapshots__/visitor-keys.js.snap
@@ -900,9 +900,10 @@ exports[`visitor keys estree 1`] = `
     "literal",
   ],
   "TSMappedType": [
+    "constraint",
+    "key",
     "nameType",
     "typeAnnotation",
-    "typeParameter",
   ],
   "TSMethodSignature": [
     "key",