Set the clock, then you should be able to log in
My Ativ S with old AMOLED technology (Galaxy S3 Generation) definitely had burn in from the navigation bar at the bottom
Personally quite satisfied with Firefox Focus (or whatever it’s called in English, in German it’s Firefox Klar)
What happens when you connect it to a PC/Mac and open the corresponding Apple Devices management app?
EDIT: That means you have turned on Advanced Data Protection on another device with the same Apple ID