Change Collection Cover (Artwork)

Hello together, is it possible to change the collection cover? When I go to change artwork, it does not work. With the films it works, only with sets it is without function. I have already tried the following: Movieset.jpg, Movieset-poster.jpg, Movieset-folder.jpg Set.jpg, Collection.jpg, poster.jpg, folder.jpg, … I also made sure that In each folder of the set the covers are the same.