You can't use Google Pay obviously if the phone is de-Googled. That's a good thing IMO, the last thing I want is Google tracking how I spend my money. Carrying a credit card in a wallet case with my phone is a very minor inconvenience.

The Bank of America app runs on Graphene without issues however. So generally speaking it is not true that banking apps don't run on de-Googled phones. Here it is the developers that are to blame if they enforce compliance with Google's requirements and don't stick to the basic FOSS version of the OS.