GDM - Setup display fractional scaling

gdm-fractional_scaling.md

1. Check if you are running X11 or Wayland:
   • echo $XDG_SESSION_TYPE
2. Copy your monitors.xml config file into GDM home directory:
   • sudo cp ~/.config/monitors.xml ~gdm/.config/monitors.xml
   • sudo chown gdm:gdm ~gdm/.config/monitors.xml
3. Access GDM's shell:
   • sudo machinectl shell gdm@ /bin/bash
4. Enable scale-monitor-framebuffer experimental feature:
   • On Wayland: gsettings set org.gnome.mutter experimental-features "['scale-monitor-framebuffer']"
   • On X11: gsettings set org.gnome.mutter experimental-features "['x11-randr-fractional-scaling']"

P.S. Arch based distros needs this patch for the X11 solution.

After trying without success multiple variations of step 2 I was guessing I was missing the gnome setting enabling fractional scaling, and didn't know how to access those for a user with no login option. Thanks a lot for the tip! :D

The provided value is outside of the valid range

You need to install 'mutter-x11-scaling' from the AUR or the Manjaro package manager, then you can set the experimental features.