Not sure who needs to read this, but if like me you're using Android Auto with your LineageOS/other libre OS smartphone, you probably need to go to Android Auto's development settings (click 10x on Android Auto's version number) > "Allow apps from unknown sources", so that apps from Aurora Store/F-Droid can connect correctly to Android Auto. I used to have "Media Unavailable" whenever I tried to play things on my car, and this fixed it.
Pretty sure it requires GApps, I don't believe Android Auto needs internet access to work but it requires regular updates on several Google apps