6 files declare their use of WebformSubmissionStorageInterface in Webform 6.x

Webform.php in src/Entity/Webform.php

WebformEntityAccessControlHandlerTest.php in tests/src/Unit/WebformEntityAccessControlHandlerTest.php

WebformEntitySettingsSubmissionsForm.php in src/EntitySettings/WebformEntitySettingsSubmissionsForm.php

WebformMessageManagerTest.php in tests/src/Unit/WebformMessageManagerTest.php

WebformSubmissionPurgeApiTest.php in tests/src/Kernel/WebformSubmissionPurgeApiTest.php

WebformSubmissionStorageTest.php in tests/src/Kernel/WebformSubmissionStorageTest.php