20 files declare their use of StreamWrapperManager in Drupal 9

config.module in core/modules/config/config.module

Allows site administrators to modify configuration.

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

file.api.php in core/lib/Drupal/Core/File/file.api.php

Hooks related to the File management system.

FileCopy.php in core/modules/migrate/src/Plugin/migrate/process/FileCopy.php

FileSystem.php in core/lib/Drupal/Core/File/FileSystem.php

FileUrlGenerator.php in core/lib/Drupal/Core/File/FileUrlGenerator.php

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

HtaccessWriter.php in core/lib/Drupal/Core/File/HtaccessWriter.php

image.module in core/modules/image/image.module

Exposes global functionality for creating image styles.

ImageFieldDisplayTest.php in core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php

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

ImageStyleCustomStreamWrappersTest.php in core/modules/image/tests/src/Kernel/ImageStyleCustomStreamWrappersTest.php

ImageStyleDownloadController.php in core/modules/image/src/Controller/ImageStyleDownloadController.php

ImageStylesPathAndUrlTest.php in core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php

locale.translation.inc in core/modules/locale/locale.translation.inc

Common API for interface translation.

MimeTypeGuesserTest.php in core/tests/Drupal/Tests/Core/File/MimeTypeGuesserTest.php

StreamWrapperManagerTest.php in core/tests/Drupal/KernelTests/Core/StreamWrapper/StreamWrapperManagerTest.php

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

ThemeTest.php in core/modules/system/tests/src/Functional/System/ThemeTest.php

UserPictureTest.php in core/modules/user/tests/src/Functional/UserPictureTest.php