Go to the online updater, hit the “Update Core Info Files”, let it finish and try again.
It’s worth noting that the Play Store version of RetroArch is a bit kneecapped by some Google restrictions, I don’t know if that’s the root of your issue but can try grabbing the apk from their website or from F-Droid.

If that doesn’t work, try Lemuroid. It’s an easier to use interface on top of a couple RetroArch cores