Feishin on Desktop. Symfonium on phone. (I can also recommend Tempo, which is open source but doesn’t work over Android Auto last I tried.) To host my music I use Navidrome. Which I have setup as a docker container, behind a reverse proxy. The files are stored on my NAS. To access remotely I have Wireguard setup. That being said, to use Android Auto with Symfonium while my Navidrome is only accessible on my network or over VPN I use split tunneling otherwise Android Auto throws a fit.