I don't see where this document supports your answer (though of course that doesn't mean your answer is wrong).
Say I have two devices, one with iOS 15 and one that's too old to support it. What I have learned so far is that if someone tries to add me as a recovery contact, they will be turned down with a note that I must update all of my devices to iOS 15 first or log out the ones running earlier versions of iOS.
So let's assume I log out on my old device. I can then become someone else's recovery contact. What will happen if I now try to log in with the old device again? Will I be blocked because I am acting as someone's recovery contact? If not, what was the point in forcing me to log out in the first place?