Application menus

My new laptop XPS 13 9370 is great but I can ran it with such high display resolution (3840 x 2160 pixel 331 PPI) that I have to run it with a scale factor of 2.12. But not all applications scale appropriately. For Gimp I could solve it using a theme with larger icons, but some old X11 applications like Xfig, which I've been using since my Unix times in the late 1980s and could never substitute by anything else, don't scale at all. This is a problem since the menus and icons, as well as line thickness and such, are so small and thin that Xfig becomes unusable.