Another alternative (temporary or permanent) solution is to use a different display manager.
I have just experienced a broken sddm, although I don’t use kde session. I replaced SDDM with Light DM and everything works fine.
# Install lightdm, if not on your system
sudo pacman -S --needed lightdm lightdm-gtk-greeter lightdm-gtk-greeter-settings
sudo systemctl disable sddm
sudo systemctl enable --now lightdm