ok so the driver is being loaded…
so install again optimus:
edit your sddm.conf:
kate /etc/sddm.conf
and put a # before the line starting with DisplayCommand and the one starting with DisplayStopCommand - you may not have this display command lines there, so proceed with install:
sudo pacman -S optimus-manager optimus-manager-plasma
dont install any dependencies, only these 2 packages;
reboot