diff --git a/pkg/analysis_server/lib/src/computer/computer_highlights.dart b/pkg/analysis_server/lib/src/computer/computer_highlights.dart
index 01274279120..084f22e3513 100644
--- a/pkg/analysis_server/lib/src/computer/computer_highlights.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_highlights.dart
@@ -1144,11 +1144,7 @@ class _DartUnitHighlightsComputerVisitor extends RecursiveAstVisitor<void> {
 
   @override
   void visitMixinDeclaration(MixinDeclaration node) {
-    computer._addRegion_token(node.sealedKeyword, HighlightRegionType.BUILT_IN);
     computer._addRegion_token(node.baseKeyword, HighlightRegionType.BUILT_IN);
-    computer._addRegion_token(
-        node.interfaceKeyword, HighlightRegionType.BUILT_IN);
-    computer._addRegion_token(node.finalKeyword, HighlightRegionType.BUILT_IN);
     computer._addRegion_token(node.mixinKeyword, HighlightRegionType.BUILT_IN);
     super.visitMixinDeclaration(node);
   }
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
index 46e43cd8b3d..902da6b8ffc 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/local_library_contributor.dart
@@ -120,9 +120,6 @@ class LibraryElementSuggestionBuilder extends GeneralizingElementVisitor<void> {
     if (node is ImplementsClause &&
         !element.isImplementableIn(request.libraryElement)) {
       return;
-    } else if (node is WithClause &&
-        !element.isMixableIn(request.libraryElement)) {
-      return;
     }
     _visitInterfaceElement(element);
   }
diff --git a/pkg/analysis_server/lib/src/services/correction/dart/convert_class_to_mixin.dart b/pkg/analysis_server/lib/src/services/correction/dart/convert_class_to_mixin.dart
index f587413f56f..7789b37f7d1 100644
--- a/pkg/analysis_server/lib/src/services/correction/dart/convert_class_to_mixin.dart
+++ b/pkg/analysis_server/lib/src/services/correction/dart/convert_class_to_mixin.dart
@@ -30,6 +30,11 @@ class ConvertClassToMixin extends CorrectionProducer {
         .any((member) => member is ConstructorDeclaration)) {
       return;
     }
+    if (classDeclaration.finalKeyword != null ||
+        classDeclaration.interfaceKeyword != null ||
+        classDeclaration.sealedKeyword != null) {
+      return;
+    }
     var finder = _SuperclassReferenceFinder();
     classDeclaration.accept(finder);
     var referencedClasses = finder.referencedClasses;
diff --git a/pkg/analysis_server/lib/src/services/refactoring/move_top_level_to_file.dart b/pkg/analysis_server/lib/src/services/refactoring/move_top_level_to_file.dart
index 035e759285c..e24e9862ffe 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/move_top_level_to_file.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/move_top_level_to_file.dart
@@ -225,9 +225,6 @@ class MoveTopLevelToFile extends RefactoringProducer {
           validSelection(node.name)) {
         name = node.name.lexeme;
       } else if (node is MixinDeclaration && validSelection(node.name)) {
-        if (node.sealedKeyword != null) {
-          sealedDeclarations.add(node);
-        }
         name = node.name.lexeme;
       } else if (node is TopLevelVariableDeclaration) {
         var variables = node.variables.variables;
@@ -410,7 +407,7 @@ class _MembersToMove {
   }
 }
 
-/// A helper to for matching sealed classes/mixins to their subclasses.
+/// A helper to for matching sealed classes to their subclasses.
 class _SealedSubclassIndex {
   final CompilationUnit unit;
 
@@ -499,9 +496,6 @@ class _SealedSubclassIndex {
     return const [];
   }
 
-  bool _isSealed(Element element) {
-    var isSealedClass = element is ClassElement && element.isSealed;
-    var isSealedMixin = element is MixinElement && element.isSealed;
-    return isSealedClass || isSealedMixin;
-  }
+  bool _isSealed(Element element) =>
+      element is ClassElement && element.isSealed;
 }
diff --git a/pkg/analysis_server/test/analysis/get_hover_test.dart b/pkg/analysis_server/test/analysis/get_hover_test.dart
index 1cdb6f44d8b..5c363d98e1f 100644
--- a/pkg/analysis_server/test/analysis/get_hover_test.dart
+++ b/pkg/analysis_server/test/analysis/get_hover_test.dart
@@ -1229,26 +1229,6 @@ base mixin A {}
     expect(hover.propagatedType, isNull);
   }
 
-  Future<void> test_mixin_declaration_final() async {
-    newFile(testFilePath, '''
-final mixin A {}
-''');
-    var hover = await prepareHover('A');
-    expect(hover.elementDescription, 'final mixin A on Object');
-    expect(hover.staticType, isNull);
-    expect(hover.propagatedType, isNull);
-  }
-
-  Future<void> test_mixin_declaration_interface() async {
-    newFile(testFilePath, '''
-interface mixin A {}
-''');
-    var hover = await prepareHover('A');
-    expect(hover.elementDescription, 'interface mixin A on Object');
-    expect(hover.staticType, isNull);
-    expect(hover.propagatedType, isNull);
-  }
-
   @failingTest
   Future<void> test_mixin_reference() async {
     newFile(testFilePath, '''
diff --git a/pkg/analysis_server/test/analysis/notification_highlights2_test.dart b/pkg/analysis_server/test/analysis/notification_highlights2_test.dart
index e97caea095a..f42b259185c 100644
--- a/pkg/analysis_server/test/analysis/notification_highlights2_test.dart
+++ b/pkg/analysis_server/test/analysis/notification_highlights2_test.dart
@@ -242,7 +242,6 @@ void f() {
   Future<void> test_BUILT_IN_final() async {
     addTestFile('''
 final class A {}
-final mixin M {}
 final class B = Object with M;
 void f() {
   var final = 42;
@@ -250,7 +249,6 @@ void f() {
 ''');
     await prepareHighlights();
     assertHasRegion(HighlightRegionType.BUILT_IN, 'final class A');
-    assertHasRegion(HighlightRegionType.BUILT_IN, 'final mixin M');
     assertHasRegion(HighlightRegionType.BUILT_IN, 'final class B');
     assertNoRegion(HighlightRegionType.BUILT_IN, 'final = 42');
   }
@@ -319,7 +317,6 @@ void f() {
   Future<void> test_BUILT_IN_interface() async {
     addTestFile('''
 interface class A {}
-interface mixin M {}
 interface class B = Object with M;
 void f() {
   var interface = 42;
@@ -327,7 +324,6 @@ void f() {
 ''');
     await prepareHighlights();
     assertHasRegion(HighlightRegionType.BUILT_IN, 'interface class A');
-    assertHasRegion(HighlightRegionType.BUILT_IN, 'interface mixin M');
     assertHasRegion(HighlightRegionType.BUILT_IN, 'interface class B');
     assertNoRegion(HighlightRegionType.BUILT_IN, 'interface = 42');
   }
@@ -437,7 +433,6 @@ void f() {
   Future<void> test_BUILT_IN_sealed() async {
     addTestFile('''
 sealed class A {}
-sealed mixin M {}
 sealed class B = Object with M;
 void f() {
   var sealed = 42;
@@ -445,7 +440,6 @@ void f() {
 ''');
     await prepareHighlights();
     assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed class A');
-    assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed mixin M');
     assertHasRegion(HighlightRegionType.BUILT_IN, 'sealed class B');
     assertNoRegion(HighlightRegionType.BUILT_IN, 'sealed = 42');
   }
diff --git a/pkg/analysis_server/test/services/completion/dart/location/implements_clause_test.dart b/pkg/analysis_server/test/services/completion/dart/location/implements_clause_test.dart
index 6bc2c04d7a1..b97bb13eebd 100644
--- a/pkg/analysis_server/test/services/completion/dart/location/implements_clause_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/location/implements_clause_test.dart
@@ -143,9 +143,6 @@ suggestions
   Future<void> test_mixin_inside() async {
     await computeSuggestions('''
 base mixin FooBase {}
-interface mixin FooInterface {}
-final mixin FooFinal {}
-sealed mixin FooSealed {}
 class A implements ^
 ''');
 
@@ -153,12 +150,6 @@ class A implements ^
 suggestions
   FooBase
     kind: mixin
-  FooFinal
-    kind: mixin
-  FooInterface
-    kind: mixin
-  FooSealed
-    kind: mixin
 ''');
   }
 
@@ -178,63 +169,6 @@ suggestions
     } else {
       assertResponse('''
 suggestions
-''');
-    }
-  }
-
-  Future<void> test_mixin_outside_final() async {
-    newFile('$testPackageLibPath/a.dart', 'final mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A implements ^
-''');
-
-    if (isProtocolVersion1) {
-      assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-    } else {
-      assertResponse('''
-suggestions
-''');
-    }
-  }
-
-  Future<void> test_mixin_outside_interface() async {
-    newFile('$testPackageLibPath/a.dart', 'interface mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A implements ^
-''');
-
-    assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-  }
-
-  Future<void> test_mixin_outside_sealed() async {
-    newFile('$testPackageLibPath/a.dart', 'sealed mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A implements ^
-''');
-
-    if (isProtocolVersion1) {
-      assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-    } else {
-      assertResponse('''
-suggestions
 ''');
     }
   }
diff --git a/pkg/analysis_server/test/services/completion/dart/location/with_clause_test.dart b/pkg/analysis_server/test/services/completion/dart/location/with_clause_test.dart
index 06046c45bf8..1dde2d27aec 100644
--- a/pkg/analysis_server/test/services/completion/dart/location/with_clause_test.dart
+++ b/pkg/analysis_server/test/services/completion/dart/location/with_clause_test.dart
@@ -94,12 +94,9 @@ suggestions
     }
   }
 
-  Future<void> test_mixin_inside() async {
+  Future<void> test_mixin_base_inside() async {
     await computeSuggestions('''
 base mixin FooBase {}
-interface mixin FooInterface {}
-final mixin FooFinal {}
-sealed mixin FooSealed {}
 class A with ^
 ''');
 
@@ -107,16 +104,10 @@ class A with ^
 suggestions
   FooBase
     kind: mixin
-  FooFinal
-    kind: mixin
-  FooInterface
-    kind: mixin
-  FooSealed
-    kind: mixin
 ''');
   }
 
-  Future<void> test_mixin_outside_base() async {
+  Future<void> test_mixin_base_outside() async {
     newFile('$testPackageLibPath/a.dart', 'base mixin Foo {}');
     await computeSuggestions('''
 import 'a.dart';
@@ -130,70 +121,7 @@ suggestions
 ''');
   }
 
-  Future<void> test_mixin_outside_final() async {
-    newFile('$testPackageLibPath/a.dart', 'final mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A with ^
-''');
-
-    if (isProtocolVersion1) {
-      assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-    } else {
-      assertResponse('''
-suggestions
-''');
-    }
-  }
-
-  Future<void> test_mixin_outside_interface() async {
-    newFile('$testPackageLibPath/a.dart', 'interface mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A with ^
-''');
-
-    if (isProtocolVersion1) {
-      assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-    } else {
-      assertResponse('''
-suggestions
-''');
-    }
-  }
-
-  Future<void> test_mixin_outside_sealed() async {
-    newFile('$testPackageLibPath/a.dart', 'sealed mixin Foo {}');
-    await computeSuggestions('''
-lib B;
-import 'a.dart';
-class A with ^
-''');
-
-    if (isProtocolVersion1) {
-      assertResponse('''
-suggestions
-  Foo
-    kind: mixin
-''');
-    } else {
-      assertResponse('''
-suggestions
-''');
-    }
-  }
-
-  Future<void> test_mixinClass_inside() async {
+  Future<void> test_mixinClass_base_inside() async {
     await computeSuggestions('''
 base mixin class FooBaseMixinClass {}
 mixin class FooMixinClass {}
@@ -209,7 +137,7 @@ suggestions
 ''');
   }
 
-  Future<void> test_mixinClass_outside() async {
+  Future<void> test_mixinClass_base_outside() async {
     newFile('$testPackageLibPath/a.dart', '''
 base mixin class FooBaseMixinClass {}
 mixin class FooMixinClass {}
diff --git a/pkg/analysis_server/test/src/services/correction/assist/convert_class_to_mixin_test.dart b/pkg/analysis_server/test/src/services/correction/assist/convert_class_to_mixin_test.dart
index 59c1bea883c..9693592fc50 100644
--- a/pkg/analysis_server/test/src/services/correction/assist/convert_class_to_mixin_test.dart
+++ b/pkg/analysis_server/test/src/services/correction/assist/convert_class_to_mixin_test.dart
@@ -375,10 +375,7 @@ mixin D on B implements A, C {
 class A {}
 final class B implements A {}
 ''');
-    await assertHasAssistAt('B', '''
-class A {}
-final mixin B implements A {}
-''');
+    await assertNoAssistAt('B');
   }
 
   Future<void> test_implements() async {
@@ -422,10 +419,7 @@ mixin A {}
 class A {}
 sealed class B extends A {}
 ''');
-    await assertHasAssistAt('B', '''
-class A {}
-sealed mixin B implements A {}
-''');
+    await assertNoAssistAt('B');
   }
 
   Future<void> test_sealed_extendsWith_super_extends() async {
@@ -442,19 +436,7 @@ sealed class C extends A with B {
   }
 }
 ''');
-    await assertHasAssistAt('C', '''
-class A {
-  a() {}
-}
-mixin class B {
-  b() {}
-}
-sealed mixin C on A implements B {
-  c() {
-    super.a();
-  }
-}
-''');
+    await assertNoAssistAt('C');
   }
 
   Future<void> test_typeParameters() async {
diff --git a/pkg/analysis_server/test/src/services/refactoring/move_top_level_to_file_test.dart b/pkg/analysis_server/test/src/services/refactoring/move_top_level_to_file_test.dart
index d8bae7afcef..9472e15b0d8 100644
--- a/pkg/analysis_server/test/src/services/refactoring/move_top_level_to_file_test.dart
+++ b/pkg/analysis_server/test/src/services/refactoring/move_top_level_to_file_test.dart
@@ -602,100 +602,6 @@ class SubSubclass extends SealedSubclass {}
         newFileContent: newFileContent);
   }
 
-  Future<void> test_sealedMixin_implements() async {
-    var originalSource = '''
-sealed mixin [!Either!] {}
-
-class Left implements Either {}
-mixin Right implements Either {}
-
-class Neither {}
-''';
-    var modifiedSource = '''
-
-class Neither {}
-''';
-    var newFileName = 'either.dart';
-    var newFileContent = '''
-sealed mixin Either {}
-
-class Left implements Either {}
-mixin Right implements Either {}
-''';
-    await _multipleDeclarations(
-        originalSource: originalSource,
-        modifiedSource: modifiedSource,
-        count: 3,
-        newFileName: newFileName,
-        newFileContent: newFileContent);
-  }
-
-  Future<void> test_sealedMixin_on_subclass() async {
-    addTestSource('''
-sealed mixin SealedMixin {}
-
-mixin [!OtherMixin!] on SealedMixin {}
-''');
-    await initializeServer();
-    await expectNoCodeAction(null);
-  }
-
-  Future<void> test_sealedMixin_on_superclass() async {
-    var originalSource = '''
-sealed mixin [!SealedMixin!] {}
-
-mixin MixinToMove on SealedMixin {}
-
-mixin MixinToStay on MixinToMove {}
-''';
-    var modifiedSource = '''
-import 'package:test/sealed_mixin.dart';
-
-
-mixin MixinToStay on MixinToMove {}
-''';
-    var newFileName = 'sealed_mixin.dart';
-    var newFileContent = '''
-sealed mixin SealedMixin {}
-
-mixin MixinToMove on SealedMixin {}
-''';
-    await _multipleDeclarations(
-        originalSource: originalSource,
-        modifiedSource: modifiedSource,
-        count: 2,
-        newFileName: newFileName,
-        newFileContent: newFileContent);
-  }
-
-  Future<void> test_sealedMixin_with() async {
-    var originalSource = '''
-sealed mixin [!Either!] {}
-
-class Left with Either {}
-class Right with Either {}
-
-class Neither {}
-''';
-    var modifiedSource = '''
-
-class Neither {}
-''';
-    var newFileName = 'either.dart';
-    var newFileContent = '''
-sealed mixin Either {}
-
-class Left with Either {}
-class Right with Either {}
-''';
-    await _multipleDeclarations(
-        originalSource: originalSource,
-        modifiedSource: modifiedSource,
-        count: 3,
-        newFileName: newFileName,
-        newFileContent: newFileContent);
-  }
-
   Future<void> test_single_class_withTypeParameters() async {
     var originalSource = '''
 class A {}