Another daily GrapheneOS driver here. I've kept banking apps off my phone anyway, and I do banking via desktop/website (I don't understand why people need to do banking 'on the go') and just use a physical credit card for tap payments when I'm out and about.

I do have older Android devices that I have run banking apps on, that I can revert to if necessary, but there's a fair bit of inconvenience I would be happy to endure to avoid being forced into that final option.

What I would recommend is a slow transition, and just start using it at home. If you have GrapheneOS on it's most paranoid settings (exploit protections) there will be exceptions you'll need to allow for a few apps.