I already used Mint for one year, but never used Arch, so I know a bit about Linux.
Anyway, as said in the title, I have 2 GPUs, the one from the AMD CPU (AMD ATI Renoir) and a GeForce GTX 1650Ti. I managed to installed the Nvidia drivers (460.56) trough the installer from Nvidias website (Blender can use the GPU). Problem is, my laptop screen isn't working. It only shows the OS on the external monitor, and the laptop screen isn't recognized in the settings, but the backlit is on.
Note: Laptop screen is wired to the AMD & Nvidia card. Every screen output (USB-C and HDMI) are wired to the Nvidia card.
Use instructions for removal from the source of this driver.
I can't help.
If you have instructions for terminal (commands), it could be better if you logout your GUI session and switch to TTY, login and run removal commands.
Okay, good and bad news.
I managed to get both screens working with mhwd by typing sudo mhwd -i pci video-chaotic-optimus-manager-tkg in the terminal. But now comes a new issue, my external screen has screen tearing (it's not G-Sync neither FreeSync), and my laptop screen is not running 120Hz, even tough the settings say it's 120Hz.
Welcome to the Optimus world of pain, where sometimes, for no apparent reason, things don't work properly.
Have a read through PRIME - ArchWiki and see if any of the troubleshooting areas sound useful. It might also be worth trying switching to the standard kernel and profile rather than the TKG kernel and profile.