Fullscreen toggle not working

I'm trying to use triple monitors and in the basic graphics options page, it has fullscreen greyed out and unable to be changed to windowed or fullscreen borderless. I've tried resetting my settings and even have reinstalled the game. Still won't let me change this setting. Is there a simple fix to this? What am I missing? I bough triple monitors pretty much specifically for this game as it is the one sim title I play without track IR support.