18 files declare their use of AccessibleInterface in Drupal 9

AccessGroupAnd.php in core/modules/block_content/src/Access/AccessGroupAnd.php

AccessibleTestingTrait.php in core/modules/block_content/tests/src/Unit/Access/AccessibleTestingTrait.php

BlockContentAccessHandlerTest.php in core/modules/block_content/tests/src/Kernel/BlockContentAccessHandlerTest.php

BlockContentGetDependencyEvent.php in core/modules/block_content/src/Event/BlockContentGetDependencyEvent.php

EntityAccessCheckTest.php in core/tests/Drupal/Tests/Core/Entity/EntityAccessCheckTest.php

EntityAccessControlHandlerTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityAccessControlHandlerTest.php

EntityInterface.php in core/lib/Drupal/Core/Entity/EntityInterface.php

FieldItemListInterface.php in core/lib/Drupal/Core/Field/FieldItemListInterface.php

HelpSearch.php in core/modules/help_topics/src/Plugin/Search/HelpSearch.php

HelpSearchPluginTest.php in core/modules/help_topics/tests/src/Kernel/HelpSearchPluginTest.php

LayoutPreviewAccessAllowed.php in core/modules/layout_builder/src/Access/LayoutPreviewAccessAllowed.php

NodeSearch.php in core/modules/node/src/Plugin/Search/NodeSearch.php

RefinableDependentAccessInterface.php in core/modules/block_content/src/Access/RefinableDependentAccessInterface.php

RefinableDependentAccessTrait.php in core/modules/block_content/src/Access/RefinableDependentAccessTrait.php

SearchPageAccessControlHandler.php in core/modules/search/src/SearchPageAccessControlHandler.php

SectionStorageInterface.php in core/modules/layout_builder/src/SectionStorageInterface.php

user.module in core/modules/user/user.module

Enables the user registration and login system.

UserSearch.php in core/modules/user/src/Plugin/Search/UserSearch.php