I'm all in favor of voting with your wallet, though easier said then done when your mortgage, long-term saving accounts, etc. are tied up with your bank account.
That said, my banking and credit card apps work fine on GrapheneOS.
Not possible in Finland. :( I'm using the one bank (OP) that used to allow rooted devices to use their app, but even they eventually blocked it via SafetyNet.
That's the kicker, they will all eventually block it, so it's not worth your time and sanity constantly swapping banks on the hopes this one will keep lax security.
That said, my banking and credit card apps work fine on GrapheneOS.