Full screen optimisation is forced on by the game, even when you tick the box in the .exe to disable it. It gives you input lag and I have fixed frametime stutters in BO4 by disabling it (which is the same problem I get in Apex).
All the threads about it are just people saying use ALT+ENTER. This isn't anything to do with FSO, thats just putting the game into full screen mode.
You know its still in full screen optimisation because if you use your volume it will come up over the game, if FSO is disabled you won't see it. Also when you tab out it won't just instantly tab, it will flash black.
Does anybody actually know if this is even fixable, I can't find anywhere where it has been mentioned by devs or anybody working for Respawn.