Just to add the Steps, in case anyone wants to try 21:9 ... You have to edit the Fallout4Prefs.ini in the Documents>My Games>Fallout4 folder and set the values of iSize H=1080 iSize W=2560 (for example). I run it in Fullscreen mode (taking up the entire screen) by using bMaximizeWindow=0 bBorderless=0 bFull Screen=1 in there as well (this is all under the DISPLAY category). If your monitor doesn't fully support that resolution in Fullscreen Mode, turn off the Full Screen portion (make it zero) and it will display in a window across your screen (eg. if you are running 2560x1440 as your Desktop Resolution). HTH