+1 for MusicAssistant. I have been using it for about 2 weeks with Plex as the source, but MA as the player after "we" (my wife) decided Spotify is too expensive.

Handing off between devices is my current pain point with it. It can group players so that you can do multi-room synced play, but I use that to hand off from my desktop to my phone. You can transfer the active playlist to another device. But in either case it's a manual interaction and doesn't "just happen". To be fair, I didn't have 100% success rate with Spotify doing this correctly either. Sometimes it did it, sometimes it just started in its own world.

The MA IOS app is REALLY rough; but I have had very good success with Xonara on ios, which is currently available through testflight.