“For the Iommu Group do I have to do everything inside the grub cmd of the usb linux live distro (I have to paste the #!/bin/bash part)?” : No. Boot into any linux live distro, use the standard terminal emulator to create a script and execute it.
“And if yes how can I deal with my OS being LUKS encrypted?”: Irrelevant, you don’t need to access anything on your OS for this step
“From what I understood this means this will allow up to 2 GB of ram to your gpu passtrough HVM qube, then I don’t understand how people in other threads have straight up 4090s working. (And what about the VRAM?)”: No, you have access to all the ram you want and don’t have any kind of limitation on VRAM.
Also, what’s the deal with the max-ram-below-4g?: You can read differents threads here:
or search on internet. Not everything is understood about what is going on with TOLUD