So yeah, Cover View is a long standing issue with MC for Mac. It's been broken for quite some time. I'm not even sure that's it's much of a great feature to have though. If you just want an album cover (and nothing else, including no text or anything), then use Display View instead (Command-3).
Also, the latest builds of MC22 for Mac (for a month or two now) have included Theater View. Theater View is a whole thing of it's own with menus and it's own interface. But it has a really neat view that you might be interested in. Navigate to Audio > Playing Now. You'll see an image of your cover art, PLUS the song name, artist, etc. After 10 or 15 seconds, the cover will disappear and images of the Artist that is playing will appear. These change every 10 or 15 seconds. This is a pretty pleasant slide show of Artist related images that might make a nice backdrop for music listening. Just FYI.
Brian.