I’ve been on Symfonium for ages, and it is the best experience with a music app I’ve ever had.

I’ve not tried it with plex, as I use navidrome. But I assume the experience with a plex server is just as good.

Supoort is great, the dev is super active on his own forum etc.

The app is paid though, but it’s a one time purchase. (it has a free trial!)