I have a Ubuntu 20.04 desktop running in a Xen virtual server. The screen resolution defaults to 1366×768. The display I have will do MUCH better. 1920×1080 is more comfortable.
To change the resolution, execute the following command:
$ xrandr --output Virtual-1 --panning 1920x1080 --scale 1.406x1.406
Virtual-1 is the name of the display. You can find the name of the current display by executing xrandr without any arguments.
$ xrandr
The problem with this method is that it does not persist across reboots. I put the command into a script that I can execute at will. The ideal situation would have this script executed automatically on startup.
Inspiration: https://www.reddit.com/r/thinkpad/comments/2g933a/howto_scale_any_1366x768_display_to_1080p/