I regularly live with a dumbphone. All it can really do is makes calls and text. Its only difficult if you give a shit about social media and chat apps. I don't so its easy
I have no actual idea, but I don't think so as it's an "online" bank where you set up the account on the mobile app. There's no other way to set up an account with this bank.
Oh. Here in France, even online banks still have web apps.
Anyway the assumption that every user has a smartphone is now very prevalent and it's going to get harder and harder to not have one, but I really want to go against the trend.