Be careful, 2FA still has issues at the moment: https://github.com/LemmyNet/lemmy/issues/3309

I seem to be having the same issue on one instance, but was able to get 2FA on a few others, so maybe just a version thing. Still bothers me that i can’t get it enabled somewhere.

Supposedly, if you click on the 2FA link on a mobile, it will launch your 2FA app to capture the info. But if that doesn’t happen, you can right click on the button, and copy the secret to create a record in your 2FA app manually. The app has to support SHA-256, so I think pretty much Authy, Microsoft Authenticator, Google authenticator, etc. are out. Supporting apps include 2FAS and Aegis.

If this can’t be done, you should click Remove 2FA and save. Otherwise, you might loose your account. On some instances and on Firefox, you may want to do this with all the extensions disabled. Some extension seems to somehow get you logged out clicking refresh.