I think that your topic is the universal secret of a big conspiracy =)
I also encountered a similar problem, I cannot change the resolution inside Linux HVM above the screen resolution of 1920X1080. I tried a bunch of things, just like you created a topic on the forum, but no one could help me.
Interestingly, I previously used Qubes OS 4.1.2 and had no problems with the screen resolution in Linux HVM. I recently installed Qubes OS 4.2.0 and was faced with the fact that it is not possible to change the screen resolution higher than 1920X1080 inside Linux HVM .
So my brother in misfortune tell me which version of Qubes OS are you using?