20.04 – Accessibility: Use high offscreen resolution to get better zoom quality? (compiz, gnome-shell)

I’m visually impaired and using Ubuntu 20.04.
Wondering if it is possible to set a higher than monitor resolution (eg: 4k root window for a 2k display).
If I understand correctly, the application windows will be rendered in offscreen textures with the high 4k resolution. Then, the compositing manager (gnome-shell, compiz) will map them to the 2k monitor display.
This would mean that when you zoom on a window you could get a better quality (the rescale would map a bigger texture to the monitor). eg: with a 4k for 2k setup and a x2 zoom you would still have a perfect one for one pixel scale between offscreen and monitor.
I guess this is not a big issue for most of you but I’m using high zoom factors and I’m getting very fuzzy results that are making things even harder to read. (the OpenGL antialias is great but it cannot guess the “missing” pixels when you zoom at x5 and you loose a lot of sharpness)

I’ve tried xrandr but did not seen any change. I’m not even sure it is still relevant on my 20.04 system:

 xrandr --output HDMI-0 --mode 3840x2160 --scale 2.0x2.0

BTW: I’ve tried gnome-shell but had to switch back to compiz to get the mandatory “zoom with mouse-wheel” option of enhanced-zoom.

Thank you for your help.