I recently got into reviving old tech and was looking at a Nokia 3210. The main challenge is that these only work on 2G which is getting shut down in more and more countries across the world.

There are 4G mainboards you can buy and projects like https://www.nokia3310lteproject.com that aim to bring them into the modern world but for me these don't go far enough as they try to preserve the original UI. For me, the ideal device would be a 4G/GPS/Wi-Fi/Bluetooth-capable Nokia brick with modern interpretations of apps for maps, music, messaging etc. with optimized user interfaces for the limited screen space their tiny LCDs offer.

TOTP at least should be doable on pretty old/basic stuff. I saw someone make a TOTP app for 3DS. Maybe a literal 15 year old Nokia is pushing it, though. This wouldn't cover SMS MFA or the one where you need to hit a button from a specific app, but ideally those would die out anyway...