There are enough non-shitty banks and credit unions, at least in the US, that you should be able to easily switch banks to a better one. They have no moat.
FWIW my US bank works on GrapheneOS and they refund all ATM fees, so you can use any ATM you want. The only issue I've run into with them is they have a Zelle integration which is only available on the phone, and on GrapheneOS it just loads to a blank white screen. But that seems to be Zelle's fault. The bank is Charles Schwab if anyone is looking for a currently-compatible-with-GrapheneOS bank in the US.
If they stopped, I think I would seriously consider swapping banks and whatever else instead of using a different OS.