It looks like you are running with Windows scaling on your end, and it looks like at 175% due to the numbers that the game is showing.
For example, 3840 divided by 1.75 = 2194 in the horizontal resolution.
All this means is that although your system is saying 3840x2160, due to the 175% scaling you are actually running at 2194x1234. This is what the game sees and because of the scaling the game lists the only compatible resolutions which in your case once again, and due to the scaling is just the one resolution of 2194x1234. When you attempt to set it to run at FULL SCREEN the game does a check and unfortunately the game graphics library that I use to handle the full screen option is simply reporting that the game cannot be run at full screen.
Manually attempting to override this will unfortunately not work either as the game does a check for this and resets it to what is actually compatible. Essentially it is not restricting you, it is just letting you know what is compatible in game and for your setup, just the one resolution and again only in windowed mode.
However, in your case since it is the one resolution it should be filling your entire screen, or very close to it and visually there is then no difference between windowed mode or full screen mode in your case.
The only thing you would miss out on is potentially some acceleration from being in a proper full screen setting, but it is very minor either way.
Hope this helps,
< Message edited by Hubert Cater -- 9/18/2019 1:01:11 AM >