I also faced this problem with the low selection of resolutions to choose for the Windows desktop with my ultrawide 3440x1440 screen. No worries, it was easily overcome with a simple modification to SeaBIOS, see here: https://groups.google.com/g/qubes-devel/c/aCCGpYysZTQ/m/4yMY...

I'm in the process of submitting a patch to SeaBIOS so it will no longer be necessary to patch this in yourself.