Ok so correct me if I am wrong, which I will happily accept and learn something new from, but I believe getting “Exclusive Fullscreen” is possible.
All you need to do is open the Starfield.ini in the My Games folder ( This PC, Documents, My Games, Starfield ) and set Borderless=1 to 0 and leave Fullscreen=1 as 1 .
As far as I can tell, this enables purely Fullscreen. The only reason I wanted this was for GSync compatibility and possibly a slight FPS bump if any at all.
Hope this helps someone, and if this doesn’t do what I assume it does please let me know!