I know it sounds a bit daft, but I was hoping to use DF as a quick and simple way to switch my triple creen set up from Nvidia Surround to Individual Monitors, and I can't get it to work.
I now believe that the DF "split" option can't run applications full screen in each split, so that didn't work.
I also tried saving the two nVidia modes as DF saved monitor profiles, (setting each up via nVidia's span option) but DF can't then switch between them, so I suppose it can't issue the neccessary nVidia commands.
I use my triple monitors for 90% of the time in spanned mode so that when most of my simultors run as "full screen" they fill the triple screens, but for 10% of the time I use xPlane11, which displays much better when it drives each of the the three monitors individually, left/centre/right, becauase that way it controls the perspective much better than as a single ultra wide screen.
I wondered if there were any xplane11 DF users that have maybe found a solution to switching easily between spanned and separate screens, or if there is another way to do it ?

Update - I may have found a compromise.....
Leave Windows and Nvidia configured as individual monitors and extended display, (so Nvidia Span is turned off).
Then I created a function on Ctl-Alt-S to move the selected display window to -1920 horizontal, 0 vertical, 300% wide and 100% high.
That enables me to force the simulation running in the window to fill the three screens. I realise you would think you could do that manually by dragging the window edges anyway, but some sims won't let you drag a window larger than the screen's max resolution (1920x1080), whereas that DF function seems to trick the sim into thinking the screen is 5760x1080.
I'm still testing, but it works with Trainz2019, which was one that wouldn't "window" bigger than 1920x1080 without nVidia span enabled...