At least BankId (digital ID thing in Sweden) and some of the Swedish banking apps don't care about if you are rooted on stock Android. I haven't tried custom ROMs in many years, but perhaps it is time for GrapheneOS these days.

Now, if you want to use your phone as a debit/credit card substitute that is different (Google Pay cares, and I don't use it thus).

Anyway, why should banking apps care? It is not like they care when I use the bank from Firefox on my Linux laptop.