18 files declare their use of ThemeManagerInterface in Drupal 9

AssetResolver.php in core/lib/Drupal/Core/Asset/AssetResolver.php

BlockListBuilder.php in core/modules/block/src/BlockListBuilder.php

BlockRepository.php in core/modules/block/src/BlockRepository.php

CurrentThemeCondition.php in core/modules/system/src/Plugin/Condition/CurrentThemeCondition.php

ElementInfoManager.php in core/lib/Drupal/Core/Render/ElementInfoManager.php

FilteredPluginManagerTrait.php in core/lib/Drupal/Core/Plugin/FilteredPluginManagerTrait.php

FilteredPluginManagerTraitTest.php in core/tests/Drupal/Tests/Core/Plugin/FilteredPluginManagerTraitTest.php

FormBuilder.php in core/lib/Drupal/Core/Form/FormBuilder.php

HtmlRenderer.php in core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php

LibraryDiscoveryCollector.php in core/lib/Drupal/Core/Asset/LibraryDiscoveryCollector.php

LibraryDiscoveryParser.php in core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php

LibraryDiscoveryParserTest.php in core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php

Contains \Drupal\Tests\Core\Asset\LibraryDiscoveryParserTest.

MenuTestController.php in core/modules/system/tests/modules/menu_test/src/Controller/MenuTestController.php

Renderer.php in core/lib/Drupal/Core/Render/Renderer.php

ThemeCacheContext.php in core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php

ThemeSettingsForm.php in core/modules/system/src/Form/ThemeSettingsForm.php

TwigExtension.php in core/lib/Drupal/Core/Template/TwigExtension.php

ViewEditForm.php in core/modules/views_ui/src/ViewEditForm.php