return of the clippy, now named skynet.

As others suggested, a simple server with a subsonic api is all you need. tailscale on it and your mobile device and you can stream with a handful of open source apps.

I am using a pi to server my music for years but been self hosting my music since google music died - never got on the spotify bandwagon.

A little docker/podman is all you need. I also work on an free android app for this purpose as well that I just posted an update to yesterday.