When looking at this screenshot it looks like there is only one monitor connected, although there are two. It's puzzling why only one monitor is shown, and how i could change settings of the second monitor. I actually had to check with xrandr that in fact two monitors are connected. It took me a while to figure out that this happens because one monitor is on top of the other in this screenshot, hiding the second monitor. It is not obvious that you have to drag the top monitor to another place such that the lower monitor is revealed.

https://i.imgur.com/vMBSo7B.png