good call asking for a proper venue to test this, but how do you mean you can’t remove federated stuff? i was under the impression (from lemmy’s homepage) that one of the features is 100% complete deletion by replacing post/comment content with ‘removed by user’. is this not the case?
these two tools apparently let you rip borrowed audiobooks from this service named libby. although i haven’t tested them. https://github.com/ping/odmpy https://github.com/bookbonobo/libby-download-extension
also, have you checked the index? stuff like this is usually there.