In this case, thanks to regulation, it seems GrapheneOS team is talking with European Commission about this problem with Play Integrity API https://fosstodon.org/@GrapheneOS@grapheneos.social/113623767380032309 and the only hope is a movement of the regulator against this policy of Google.

the problem here is not the banks or apps, the problem is Google Play Integrity API, which is supposed to enforce to run apps in secured phones and it is used to ban secured ROMs such as GrapheneOS and it allows to run apps on outdated phones without security patches.