Most likely it’s the other way around, hdmi is hardwired to the nvidia. Also see here:
Second monitor on Asus ROG Zephyrus with AMD & Nvidia graphics .
HDMI not working on mux-switch laptop .
I also believe people had better luck using envycontrol instead of optimus-manager to avoid the issue. Keep in mind that this AUR package has already been made available in the manjaro repos, it’s in testing right now:
More tools for Optimus laptops are now available .