I have over 130+ artists with 1000s of tracks all sorted and with valid metadata externally to the Music / iTune app on my Mac (Catalina). The folder layout is Artist / Album / CD in Album (ranges 1-12 currently) / Tracks (e.g. 01 - Composer - Track Name.p4a)
When I import the artist / track, Music does not apply the artwork even though its in the track metadata and stored as Folder.jpg in the source folder. The latter works on a couple of music players and Volumio on the Raspberry under the TV :-)
I'm happy to delete the whole Mac music library and start again if needed.
Though I can, if needed, hack around in Python, I'm not an Apple script creator. I could go through the whole lot and manually link the jpg to the album but does anyone know of an easier way?