Yeah all of my servers are on usff PC’s, so I get it.
If you do a hypervisor like proxmox, then throw your NVR in a VM, you can just create a couple of virtual NICs (though you’ll be back at that FW issue I’m sure).
USB NICs are pretty well supported these days though, and cheap to boot. Just need to be certain you’ve got usb3 if you want to make use of that gig though!
I’ve got a few pi-a-likes that I’m doing similar camera fun with, though using some webcams in there and a 3d printed case. At least that way they match my diy temp sensors with esp32s!
Russia was bombing civilian targets from the start.