I have my music & movies on a Mac Mini at home and run the Plex server on it (for free) and while driving or traveling I use PlexAmp on my phone to listen to my music (for free) - Plex takes care of the UPNP and so on to make this work. Now, Plex is asking for money for this service: https://www.plex.tv/blog/important-2025-plex-updates/

I think… this seems reasonable? I could run https://jellyfin.org and do it myself I guess, but might be inclined to pay a bit to avoid the extra work…