A surprising amount. Genshin and many Gatcha games are GPU intensive, even on such a small screen.

It might be because they code very inefficiently, and they might also be doing a ton of crypto and anti-hacking calculations in background, but these games are surprisingly taxing for the phone they're running on.

I think a substantial amount at least. Kids and tweens seem to game a lot on mobile, and Fortnite is a GPU-intensive game that runs on mobile.