This
get_cover_art python script can download cover art from Apple's servers and embed it into your music files. It requires python 3.5 or above, so you might have to
install that too. I found (on Monterey) that although it embeds the cover art into your individual music files, for some reason it didn't update the artwork in the album display in the Music app. It's a simple matter to correct that with 'show song info' and 'show album info' though. I haven't tried it with iTunes, but I see no reason why it shouldn't work.