Have you actually tried using your banking application on a recent (post introduction of sandboxed Google Play) GrapheneOS?
Restricting things to only Google ROMs basically also means your banking app won't work on a bunch of non-google Android phones and even most banks don't want to go that far.
Restricting things to only Google ROMs basically also means your banking app won't work on a bunch of non-google Android phones and even most banks don't want to go that far.