Cover art woes in music files

[TheDreadPirate]

FWIW, I have copied the music folder, renamed it, removed embedded art from each file, removed folder.jpg/cover.jpg and added the folder to JF.

With this, all images are blank in every one of my clients (I expect this).

Adding a 1400x1400 jpg file to that folder, called "cover.jpg", restored the blurry images shown in one of the pics above. N.B. it is the same if the art file is called "folder.jpg".

To me, this looks like embedded art is not being scanned or not processed correctly, but a parallel file in the folder is scanned and used instead.

OK, I don't necessarily need embedded art in my music for Jellyfin (or Emby) but it exists for other scenarios in my case, but what I'm not following is why JF isn't able to make a non-blurry picture for whatever purpose or size, from a perfectly fine 1400x1400 source image.  Any ideas?

Definitely don't remove embedded images.  For music Jellyfin likes embedded images and, in my experience, works better with them vs having an image in the folder.

You can use an app like Musicbrainz Picard to auto-magically tag and embedded images in a way that Jellyfin tends to like.  Because of the nature of music and how many different ways it can be organized you will still need to tweak things to get them how you like.  But Picard will do the majority of the work.