It's not a banking app, but there are definitely apps that don't work on GrapheneOS that can't be made to work. A friend of mine is "required" to use Microsoft Authenticator for his work MFA, which won't run. He's looking at having to carry another phone.

I have to use the awful thing, too, so if I go to GrapheneOS next year when, hopefully, a non-Google phone supports it, I'll have to carry two phones. Ugh.