okay so the optimus-daemon is active. please boot to the dark-screen, change to a console as before and login.
from there edit /etc/default/grub with sudo rights and edit the following:
at
GRUB_CMDLINE_LINUX_DEFAULT= .....
you add the following to the existing entries that are there
optimus-manager.startup=nvidia
store the file and run
sudo update grub
sudo mkinitcpio -P
after do a restart