I have an 11 inch Laptop and am running Qubes. I have increased the scaling and the font, but it does not affect the font in the panel or the font in the menu and both are very hard to read. I do not see a way to increase these fonts.
Is there a 150% scaling also? 200% is making some windows so large I am unable to see all the contents.
Panels should scale too, even in a such poor DE as xfce. Maybe you have a bug (scale stays 100% for panels). Try setting 200% scale and in dom0:
xfce4-panel --restart
Does it become bigger?
Another way is to use KDE instead of xfce as it supports a better scaling, icons, windows placement. Well, almost everything is better, but if you are new to Qubes OS, then you probably should not rush away from default xfce.
Dom0 (Applications)---->System Tools —> Appearance
right click xfce panel ----> Panel --Panel preferences
This is what you are looking for?
good luck