I’ve used PlexAmp. It’s shit. It tries its best, but it can’t make up for the flaws in plex’s underlying library system. It also requires having a library host running all the time. Apple host the music for me and I can make library changes from any of my devices.

I’ve tried a number of other self host options, as well, and none of them come close to the feature set in Music. I even wrote my own web app to do it way back in the 2000s, just so I could implement my own UX. This is still better.