VT-d option is present in Bios of the M720Q too, No problem for pci-e passthrough via Proxmox but regarding iGPU, it's not very stable and I can't recommend proxmox if you require this specific need. It's not an M720Q problem, iGPU passthrough is, from my knowledge, not very usable under proxmox. If you install a dedicated graphic card, it's another story and you'll get a stable solution. Other solution is to use proxmox LXC container, in this situation, iGPU works fine but I didn't like the idea.
That's the main reason I replaced proxmox by ESXi (on my M720Q), in which iGPU passthrough is working flawlessly (tested with OMV and xpeno, jellyfin hardware transcoding).
The free license is enough BUT, backup of VMs with passthrough peripherals is a pain in the *** and at the moment I didn't find a way to do so.
EDIT: the easiest way to backup an ESXi VM with passthrough peripherals and free license (aka without vCenter server), in my opinion, is to clone it. I followed this
guide and it worked fine.