Gnome seems to do that per window, not per framebuffer like macOS does. The framebuffer size seems to be exactly the display resolution, plus you need GPU to do

Gnome seems to do that per window, not per framebuffer like macOS does. The framebuffer size seems to be exactly the display resolution, plus you need GPU to do window scaling, you cannot let the output encoder to do the job. The Windows and Qt approach has it's own issues with fractional pixel positions, and the resulting problem with mapping integer input coordinates to these. And of course, it doesn't work nice with legacy apps (Gnome has to handle X11 apps, that won't tell anything about the scale they work with. See also: Gimp).