I have not followed up in the past nine months because my remote sessions are somewhat useable in the current state, but it still annoys me to no end, so I just tried looking at it some more. I do not have a solution. Here is a recap of what I have and have not figured out.
When the Windows client display preferences are set to full screen (everything else default), the remote desktop session that appears on the client's physical display thinks it is connected to the "default" video output, for which xrandr (run in a terminal window, inside the remote desktop session) shows a maximum resolution of 1920x1200, with a resolution of 1280x720 selected, which is exactly half the width and half the height of the physical display on the client (2560x1440). The xdpyinfo command reports a dpi of 75. If I set the client preferences to 192 dpi (corresponding to physical display on client), the resulting remote desktop session is still 1280x720, but all elements are scaled up by a factor of 2. It is my understanding that this is the default scaling generated by X when it detects (or is given) a dpi larger than some value that it considers to be hi-dpi.
I have seen suggestions about creating a new display section in xorg.conf on the server for a virtual monitor, but most people report that does not work. I am not knowledgeable enough to understand exactly how x2go interacts both with the X-server on the x2go server (RHEL 7.4) and with the X-server (VcXsrv) on the x2go client (Windows 10). I'm thinking that somehow, if possible, I need to change the "default" video output used by one or the other of those X-servers to allow 2560x1440 resolution. Does anyone know how to do this?
Even if I get that to work, I may still have an issue getting the MATE desktop to use my desired hi-dpi scaling (instead of just forcing everything to double). Inside the remote MATE desktop, I am not able to change any display preferences; it always produces an error related to the versions of xrandr (display preferences requires at least 1.3, server version is 1.2, though program I'm actually running is 1.5).
And would it be worth my time to try again building x2go from the Arctica project?
Jean-Paul