Monitor scaling does not work properly

I have a laptop and a monitor connected to it. I would like 125% scaling on the lapop and 100% on the monitor. Changing any settings changes the scaling on both monitors. I would like to scale 125% laptop separately. 100% monitor.

EDIT:

There are quite a few posts out there (see list below) that deal successfully with similar cases via xrandr.

Try with a command like

xrandr --output eDP-1-1 --scale 1.25x1.25 --mode 1920x1080 --fb 2400x1350 --pos 0x0 --output HDMI-0 --primary --scale 1x1 --mode 1920x1080 --right-of eDP-1-1

If this doesn't work right away, I suggest you: 1) post a detail of what you get, and 2) tinker a bit with flags, checking the references. This should be quite close to what works.

If this works, and you want to set it permanently, check Best place to automatically add mode in xrandr and links therein.

Sources:

1. Is it possible to have different DPI configurations for two different screens?
2. xrandr dual-monitor scaling issue
3. https://superuser.com/questions/522453/xrandr-dpi-on-multihead-linux
4. https://blog.jamiek.it/2015/04/manually-fixing-multiple-screens-with.html
5. https://unix.stackexchange.com/questions/253449/multiple-monitors-hidpi-scaling
6. https://www.reddit.com/r/gnome/comments/i1b2d1/x11_scaling_issues_with_multiple_monitors/
7. https://github.com/linuxmint/Cinnamon/issues/3606
8. https://bugs.launchpad.net/ubuntu/+source/mutter/+bug/1857383
9. https://wiki.archlinux.org/title/xrandr