There is a darkened circle around the edges of my screen. It does not appear in F1 mode though. As far as I can tell there is no way to disable it. It does not seem to be in previous versions. I have a comparison from 1.11.2 no F1, 1.12 no F1 and 1.12 F1. NOTE: it is taken in the same scene, but just look at the side.