Deleting Artwork in Music on Mac (Big Sur)

Hi,

I recently moved from iTunes to the Music app on my new Mac. I add the artwork always manually. However in the Music app, I do not know how to delete the artwork for an album. I can add a second artwork for the album but I don't see how I can delete one of them. There is no 'blue surrounding border' around one of them and if I click delete, nothing happens.

Can anyone help me? Many thanks in advance for your help!