i experienced that the optimus-manager-qt package can cause misbehaviour. a simple and really bullet-proof way ist to do the following steps:
a) install optimus-manager from the packet-manager
b) activate with sudo systemctl enable optimus-manager
c) open a editor with sudo-rights and edit /etc/default/grub
add to the entry GRUB_CMDLINE_LINUX_DEFAULT=" the following to the existing entries
optimus-manager.startup=nvidia nvidia_drm.modeset=1
d) after editing open a console and run the following
sudo update-grub
sudo mkinitcpio -P
e) do a reboot
f) after reboot enable the following service
sudo systemctl enable nvidia-persistenced
g) you can either start the service with sudo systemctl start nvidia-persistenced
or to be on the safe side and do another reboot (windows-style 
)
P.S.: from that point up you do have a working system with active-nvidia that is 100% working and then it’s up to you if you want to dig deeper with hybrid-mode (that depends on the hardware, sometimes no problem up to total-nightmare) and so forth, but the main problem for i think almost everyone is to get this nvidia-stuff first running and from there you are able to modify it in any way you want.