At each boot up and login the desktop is a bit zoomed (Window scaling at more than 1x but not 2x). I need to go to Appearance → Settings → Window Scaling and change from 1x (not scaling) [which is actually false, since it is scaled to probably 1.1-1.2x) to 2x and then back to 1x.
I looked on the internet but found nothing that solved the issue for me.
Using XFCE (Xfwm4 theme)
Thank you.
Welcome to the forum, @adyteo
Let’s suppose your login manager is lightdm
press CTRL+Alt+F3 at login screen
log in
yay -S ly
sudo systemctl disable lightdm
sudo systemctl enable ly
sudo reboot
you will get a simple login screen
Make your changes and
sudo systemctl disable ly
sudo systemctl enable lightdm
I think you use sddm because scaling there matters. So instead of lightdm use sddm above.
Thank you Peter. Unfortunately, it did not help, same problem.
I actually use lightdm, not sddm (Failed to enable unit: Unit sddm.service does not exist)
It is an inconvenience (for the time being) to change the appearance every time I log in but I can survive this pain 
It only started about 7-10 days before, maybe an update or a package that changed something.
and what does
xfce4-display-settings
show?