6 files declare their use of ActivityDestinationBase in Open Social 8.9

NotificationsActivityDestination.php in modules/custom/activity_basics/src/Plugin/ActivityDestination/NotificationsActivityDestination.php

SendActivityDestinationBase.php in modules/custom/activity_send/src/Plugin/SendActivityDestinationBase.php

StreamExploreActivityDestination.php in modules/custom/activity_basics/src/Plugin/ActivityDestination/StreamExploreActivityDestination.php

StreamGroupActivityDestination.php in modules/custom/activity_basics/src/Plugin/ActivityDestination/StreamGroupActivityDestination.php

StreamHomeActivityDestination.php in modules/custom/activity_basics/src/Plugin/ActivityDestination/StreamHomeActivityDestination.php

StreamProfileActivityDestination.php in modules/custom/activity_basics/src/Plugin/ActivityDestination/StreamProfileActivityDestination.php