36 files declare their use of FileInterface

CKEditor5ImageController.php in core/modules/ckeditor5/src/Controller/CKEditor5ImageController.php
claro.theme in core/themes/claro/claro.theme
Functions to support theming in the Claro theme.
ComputedFileUrlTest.php in core/modules/file/tests/src/Kernel/ComputedFileUrlTest.php
DatabaseFileUsageBackend.php in core/modules/file/src/FileUsage/DatabaseFileUsageBackend.php
EditorFileReference.php in core/modules/editor/src/Plugin/Filter/EditorFileReference.php
editor_test.module in core/modules/editor/tests/modules/editor_test/editor_test.module
Helper module for the Text Editor tests.
EntityReferenceFieldItemNormalizer.php in core/modules/serialization/src/Normalizer/EntityReferenceFieldItemNormalizer.php
file.module in core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
File.php in core/modules/media/src/Plugin/media/Source/File.php
File.php in core/modules/file/src/Entity/File.php
FileEntityNormalizer.php in core/modules/hal/src/Normalizer/FileEntityNormalizer.php
FileFieldTestBase.php in core/modules/file/tests/src/Functional/FileFieldTestBase.php
FileManagedAccessTest.php in core/modules/file/tests/src/Kernel/FileManagedAccessTest.php
FileManagedTestBase.php in core/modules/file/tests/src/Functional/FileManagedTestBase.php
FileManagedUnitTestBase.php in core/modules/file/tests/src/Kernel/FileManagedUnitTestBase.php
FileMigrationSetupTrait.php in core/modules/file/tests/src/Kernel/Migrate/d7/FileMigrationSetupTrait.php
FileSelection.php in core/modules/file/src/Plugin/EntityReferenceSelection/FileSelection.php
FileTest.php in core/modules/jsonapi/tests/src/Functional/FileTest.php
FileUploadForm.php in core/modules/media_library/src/Form/FileUploadForm.php
FileUploadHandler.php in core/modules/file/src/Upload/FileUploadHandler.php
FileUploadResource.php in core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
FileUploadResult.php in core/modules/file/src/Upload/FileUploadResult.php
FileUsageBase.php in core/modules/file/src/FileUsage/FileUsageBase.php
FileUsageInterface.php in core/modules/file/src/FileUsage/FileUsageInterface.php
image.module in core/modules/image/image.module
Exposes global functionality for creating image styles.
InlineBlockPrivateFilesTest.php in core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
LoadTest.php in core/modules/file/tests/src/Kernel/LoadTest.php
locale.bulk.inc in core/modules/locale/locale.bulk.inc
Mass import-export and batch import functionality for Gettext .po files.
MigrateFileTest.php in core/modules/file/tests/src/Kernel/Migrate/d6/MigrateFileTest.php
MigrateUserPictureD6FileTest.php in core/modules/user/tests/src/Kernel/Migrate/d6/MigrateUserPictureD6FileTest.php
ResponsiveImageFormatter.php in core/modules/responsive_image/src/Plugin/Field/FieldFormatter/ResponsiveImageFormatter.php
SpaceUsedTest.php in core/modules/file/tests/src/Kernel/SpaceUsedTest.php
Status.php in core/modules/file/src/Plugin/views/filter/Status.php
TemporaryJsonapiFileFieldUploader.php in core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
TestFileUsage.php in core/modules/system/tests/modules/service_provider_test/src/TestFileUsage.php
UrlPlainFormatter.php in core/modules/file/src/Plugin/Field/FieldFormatter/UrlPlainFormatter.php

Buggy or inaccurate documentation? Please file an issue. Need support? Need help programming? Connect with the Drupal community.