14 files declare their use of RequestPolicyInterface in Drupal 9

AllowToolbarPath.php in core/modules/toolbar/src/PageCache/AllowToolbarPath.php

AllowToolbarPathTest.php in core/modules/toolbar/tests/src/Unit/PageCache/AllowToolbarPathTest.php

ChainRequestPolicyTest.php in core/tests/Drupal/Tests/Core/PageCache/ChainRequestPolicyTest.php

CommandLineOrUnsafeMethod.php in core/lib/Drupal/Core/PageCache/RequestPolicy/CommandLineOrUnsafeMethod.php

CommandLineOrUnsafeMethodTest.php in core/tests/Drupal/Tests/Core/PageCache/CommandLineOrUnsafeMethodTest.php

DenyTestAuthRequests.php in core/modules/rest/tests/modules/rest_test/src/PageCache/RequestPolicy/DenyTestAuthRequests.php

DisallowBasicAuthRequests.php in core/modules/basic_auth/src/PageCache/DisallowBasicAuthRequests.php

DynamicPageCacheSubscriber.php in core/modules/dynamic_page_cache/src/EventSubscriber/DynamicPageCacheSubscriber.php

FinishResponseSubscriber.php in core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php

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

NoSessionOpen.php in core/lib/Drupal/Core/PageCache/RequestPolicy/NoSessionOpen.php

NoSessionOpenTest.php in core/tests/Drupal/Tests/Core/PageCache/NoSessionOpenTest.php

PageCache.php in core/modules/page_cache/src/StackMiddleware/PageCache.php

system.module in core/modules/system/system.module

Configuration system that lets administrators modify the workings of the site.