Firstly I bricked it like OP shows us, but then I was trying to recovery it and then hard bricked that (black screen and no indication in bluetooth menu or whatsoever). Then that warranty stuff. :D
That's because they want to separate amazfit a MI stuff probably, but yes, I don't understand it either. Especially then mi band 4 can be paired with Zepp as you said and as I know.
And that "hidden" option is visible for me even completely.
So it means it probably wont update that much if at all. And what features are missing? :O The reason why i am using Zepp (amazfit) is its automated Strava synchronization.