Right, the files downloaded by qbit has to be manually deleted but if import fails (doesn't move or create link in library folder) then jellyfin will not see it. It does show manual input required so at least it notifies you but yeah, can't automate deletion within sonarr itself. I had this issue only twice on ext and the exe does nothing on linux with good permissions anyway so didn't see a need to handle it but would be a nice security feature for microslop users.

Edit: I do see a comment mentioning enabling the fail option in indexer can delete the files after it is fully downloaded. But others say it can't so test it yourself.