Based on the same GitHub repo, I also managed to passthrough the iGPU from my Minisforum UM780 XTX with a Ryzen 7 7840HS and 780M graphics. However, I had severe trouble trying to extract the vBIOS from my 7840HS. Luckily, the 7940HS has the same 780M graphics as my 7840HS, so I could just download the vBIOS from the GitHub repo.
Just for the record, these were my steps:
Get the AMD Vendor Reset Plugin (This allows the iGPU to be re-initialized for passthrough)
Reboot Unraid
Then in Tools > System Devices, search for your iGPU and audio device (AMD/ATI) and tick the checkboxes. After, click "Bind selected to VFIO at boot"
Reboot Unraid
Create or edit your VM:
Choose "Q35-7.2" or later for the machine
For the vBIOS, use vbios_7940hs.bin
Once you started your VM and set it up, it's time to install the AMD graphics drivers. However, you need to download the offline installer, otherwise the online installer might complain that the system is not an AMD system and aborts the installation.
Profit