Plexamp is what I settled on too, before deciding that I was only going to be happy if I built something better.

Plexamp is quite good as a standalone app, but as close to greatness as it is, it's a React Native app (better than a Flutter app, but still) that doesn't play well with the iOS ecosystem — no widgets, virtually no Siri/App Intents support, no Apple Music integration, etc.

I also decided that it shouldn't matter where my music "lives", and so it supports any local, self-hosted, or cloud-based source. (These are working today: https://imgur.com/szrkeIJ)