ok I have a solution now, thanks to you all.
It now works past lightdm and as default.
To sum-up:
I followed the instructions provided by @GjMan78’s link.
here’s the link again: AltGR-WEur on Linux
which made the keyboard layout us, variant altgr-weur available to choose at lightdm login screen.
It was available but I had to manually select it at lightdm login screen each time.
then to make it the default automatically so not to have to select the variant at lightdm each time,
I followed the instructions, again provided by @GjMan78 at this arch wiki link:
https://wiki.archlinux.org/title/LightDM#Keymap
From that wiki, I tried to add this line to my ~/.Xmodmap file
-layout us -variant altgr-weur
logout out and checked if it worked. But unfortunately it didn’t. I guess I missed something.
So instead I created a file ~/.Xkbmap with the same line.
logout and checked again and it worked. The variant is the default now.
At least that’s one way to do it 
Again, thank you all for your help.