linuxmemes

Do you want the overview XML or for a specific category within virt-manager?

A full XML, unless you have something private in there, which you can remove. I just remember that for nvidia's there could be parts preventing load anywhere. In my case, for example, it was booting a BIOS VM instead of UEFI one.

shows both my GPUs are there now

But what's the driver used? Should be something like this (my laptop for example, without irrelevant lines)

01:00.0 VGA compatible controller: NVIDIA Corporation GA104 [Geforce RTX 3070 Ti Laptop GPU] (rev a1)
	Kernel driver in use: vfio-pci
01:00.1 Audio device: NVIDIA Corporation GA104 High Definition Audio Controller (rev a1)
	Kernel driver in use: vfio-pci
06:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Rembrandt (rev c7)
	Kernel driver in use: amdgpu
06:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Device 1640
	Kernel driver in use: snd_hda_intel

the BM says iommu group is not viable

Well that's something. Check the script at arch wiki on VFIO, at the paragraph "2.2 Ensuring that the groups are valid". It should print out the IOMMU groups you have in your system.

Basically, a thing with IOMMU is that you must pass all or none of the devices down to VM within each IOMMU group, even if you don't necessarily want them in your VM. In most cases, that means also passing the built-in sound card that feeds audio via HDMI outputs (the .1's in the above example). In cases where there's something else crucial in that IOMMU group, there's ACS patch but that's a hack and should only be used as a last resort.