I contacted my bank, insisting that GrapheneOS is one of the most secure OS on the market and therefore should be supported if they actually care about users' security (it's actually far more secure than all the old, far less secure but Google-approved devices out there). They acknowledged an fixed their app, one of the most popular in France.

Still missing Android Pay but that's due to Android Pay being closed. I wish banks would do something and support NFC payment systems that don't require the device to be controlled by Google (how can we be okay with this?!)