So the old music player isn't still included by default. It should still work just fine on modern android if you install it, and there's plenty of foss media players on fdroid (ie not Google-dependent), most of them thin wrappers around the android media apis with a few extras like playlists. Kodi and VLC should work fine without Google services, and LineageOS Eleven doesn't require Google, though I'm not sure if it still works on modern Android.

Lack of media playback options shouldn't be able to stop you from using AOSP.