This took forever!!
We’ve been trying to get this to work too and tried a variation of Recursoft’s approach before and could not for the life of us figure it out (we have two additional displays instead of one). But laying out the two monitors like Recursoft did in Unreal and next to each other in the display settings worked. Make the Host the width of both rosolutions and move the Node_0 over the amount of the resolution of primary monitor and turn off fullscreen. We had to change the size of the node or else it blacked out our primary monitor. Hopefully this helps someone else too!