Deleting unused files in Drupal 9

As of Drupal 8.4, files that have no remaining usages are no longer deleted by default.

You can change this in a configuration-file-only setting.

https://www.drupal.org/project/file_delete

files are still there for each revision, so to remove from being listed:

https://www.drupal.org/project/node_revision_delete

And finally (as Clay noted) https://www.drupal.org/project/auditfiles

And Unmanaged / Unused Files | Manage | Delete | Drupal.org

And Fancy File Delete | Drupal.org

Some of the solutions should be posted here:

Delete orphan files | Drupal.org