It’s time for me to move from SMS to a 2FA Authenticator app. I want something that will be open source but also ridiculously easy to back up, transfer to a new device, or replace if it is on a device that fails. I want it to be versatile enough to use across all necessary authentications. I also want to be sure that I can use the same app for many many years. I don’t want it tied into another service.

What’s my best option?