Fallout 4

If you want to fix the annoying issues with Xserver multi-monitor mouse, set your other monitor (the one you do NOT want to play on) as primary and configure the game window to run at an offset (on the monitor you want to play on). Let's say we have two monitors - the one on the left @1920x1080 set as Primary and the other (on the right, the one you actually want your game to display on) @2560x1080. Put something like this into your Fallout4.ini:

iLocation X=1920
iLocation Y=0
iPresentInterval=0
bBorderless=1
bFull Screen=0
bMaximizeWindow=1
iSize H=1080
iSize W=2560

This piece of config will offset the game window by 1920 pixels to the right, set it to 2560x1080 borderless, disable fullscreen and disable in-game v-sync. Going into the Options from the game launcher will screw these up so make sure you set your graphics options before you do these tweaks.