First and foremost ensure your system is up-to-date
sudo pacman -Syu
As it is now it could be you are using Nvidia as the primary driver - so for the iGPU to be primary at boot I suggest you ensure you have the hybrid driver installed.
You can verify if this is the case by listing installed drivers
mhwd -li
If the list do not contain video-hybrid-intel-nvidia-prime please sync it
sudo mhwd -i pci video-hybrid-intel-nvidia-prime
If you are not a gamer - you may only be needing Nvidia in edge cases - and for that you can use envycontrol. Not having Nvidia as the primary GPU will also extend the battery life.
sudo pacman -Syu envycontrol
To utilize the Nvidia card for a certain application or game - use primerun <appname> to launch it.