I’ve submitted this on as a bug report. Even my packaged (shipping) 4.11.1 builds will not go into full screen if the “Oculus VR Runtime Service” is running anywhere in the background. (Even if my Oculus hardware is not even plugged in.) I was able to reproduce this behavior even with a blank project.
If anyone else who has an Oculus is having trouble getting fullscreen working, run services.msc, find the “Oculus VR Runtime Service” and stop it. Restart your game, and you should be able to enter full screen again.