I'm not 100% sure if this corresponds with having native support for Apple silicon for games, but there is a metadata key on the Steam store for Apple silicon support.
https://steamdb.info/search/?a=app_keynames&type=-1&keyname=458&operator=3&keyvalue=&display_value=on
It'd be neat if you could pull for the key for macosapplesilicon and index way more games rather than manually do it.
Though I see some games don't have it apparently, like Among Us, however factorio and Baldur's Gate have it.
While other games, presumably without native support, have the macos64 value