Hello Aidan
Windows 10 is really a mess. Everything you can do in a reasonable simple way in XP
becomes almost impossible in Windows 10 ! All the stuff for adjusting menu fonts, title
bar fonts, window borders width, ... is gone in Windows 10, and you have to cope with the
generally aberrant values Microsoft decided for you (in fact Windows 10 was conceived for
tablets, and even if you buy the most expensive laptop or desktop computer, you end up
using a tablet...).
Fortunately, browsing the web gives some solutions, like register keys to modify, or
tweakers (Winaero Tweaker for instance) which allow to regain some control on GUI
appearance.
BUT, this is without counting with the deplorable way Windows 10 manages the scaling on
high DPI displays : if you leave Windows 10 manage the scaling, everything is blurred on
the screen, which is really a pity when you opted for a high DPI display !
The only way to go is to tell Windows 10 "Don't do anything" (an option
exists on a per application basis to have no scaling done by the OS, the scaling is done
by the application). And here is my problem : Xemacs must do all the scaling : no problem
for the text font (easy to change), fortunately the toolbar is fairly readable (at least
on my 32" monitor), but the menubar font sucks : much too large as I explained.
Now other applications have also problems, a web search with "windows 10 scaling
issues" gives you countless references to users complaining about this, and sometimes
some solutions. Sadly I didn't find anything for Xemacs native on Windows ...
To answer precisely your question, I tried to decrease the menu font size (using Winaero
Tweaker, as Windows 10 has no native way to do that). But as the Windows 10 scaling is
disabled for Xemacs (only way to have a crisp edited text), it had no effect, except
making Windows menus more difficult to read...