12 files declare their use of StreamWrapperInterface in Drupal 9

DownloadTest.php in core/modules/migrate/tests/src/Kernel/process/DownloadTest.php

DummyRemoteReadOnlyStreamWrapper.php in core/modules/file/tests/file_test/src/StreamWrapper/DummyRemoteReadOnlyStreamWrapper.php

editor.admin.inc in core/modules/editor/editor.admin.inc

Administration functions for editor.module.

FileCopyTest.php in core/modules/migrate/tests/src/Kernel/process/FileCopyTest.php

FileItem.php in core/modules/file/src/Plugin/Field/FieldType/FileItem.php

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

FunctionalTestSetupTrait.php in core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php

GDToolkit.php in core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php

ImageItem.php in core/modules/image/src/Plugin/Field/FieldType/ImageItem.php

ImageStyle.php in core/modules/image/src/Entity/ImageStyle.php

ReadOnlyStreamWrapperTest.php in core/tests/Drupal/KernelTests/Core/File/ReadOnlyStreamWrapperTest.php

TranslationsStream.php in core/modules/locale/src/StreamWrapper/TranslationsStream.php