How do I fix Apple ID login issues on my iPad Air 2?

I read a Forbes article on setting up my iCloud account for Advanced Data Protection and went through the steps. It required my signing out of my aged iPad Air2.

Now when I try to run the iPad Air 2, I get the message that I can't sign in with my Apple ID. I use it still, it still seems to run things like Gmail. But is there any way to squeeze some more months to years out of this, e.g., in resuming my ability to sign in?

[Edited by Moderator]