PearTune
Play a music collection that lives on a computer at home, from anywhere. It can be your computer or a friend's. No port forwarding, no VPN, no account and no cloud copy of your files.
Android is in early testing. Join the tester list with the Google account you use on the Play Store.
What you need
Two things: somewhere for the music to live, and the app.
The server. Any computer that stays on and holds the music - a home server appliance, a NAS, a spare desktop, a laptop that is usually awake. On Mac, Windows and Linux there is an installer that puts PearTune in the menu bar or system tray and starts it with the machine. It reads your files where they already are, straight out of a folder or from a media server you already run such as Navidrome or Jellyfin, so nothing is moved or converted. Setting up a server.
The app. iPhone first, with Android close behind. If a friend is running the library, this is the only part you need.