as an option to download the first 10 minutes. The asterisk means the numbers are treated as a timestamp instead of looking for a chapter with that title.
to my knowledge you can't get squares from yt-dlp. Strawberry Music Player has a feature to download and embed the cover from MusicBrainz, I usually use that (I have to correct the tags from yt-dlp most of the time anyways). I think Picard has that too, but I don't use that.
I don't think yt-dlp has built-in image cropping, so it's just going to download thumbnails in the resolutions provided by the server. (See the --list-thumbnails option.) To crop what you download, consider a tool like ImageMagick.