If you're playing it via Spotify, it's not your music, it's Spotify's. Waymo is cool technology but I am disappointed at how the app requires a Google account plus access to google play services on an Android phone, and how the streaming music feature requires some kind of protocol that only Spotify and some proprietary Google music app support. All of my music is stored on a personal server that I stream to my phone via Jellyfin, and this does not work in a Waymo.

It's not your music unless you own the copyright, even if its on a disc or drive.