I discovered feishin today on Github. It’s made by the creator of sonixd, another great jellyfin/subsonic desktop client.
Works super smooth. Feels basically like Spotify desktop, but FOSS.
The only missing feature for me is the ability to cache songs for offline playback.
You don’t need navidrome!
Can’t help with the mpv thing unfortunately. I just selected browser audio as the backend.
You could check the issue tracker though.