https://xcp-ng.org/docs/compute.html#vgpu
This is what you need, Pass through. Not necessarily VGPU ($400 per seat).

But! (Windows)
Follow these steps:

The link above. Do not connect the GPU to the VM you have. restart while holding shift so you can start with "safe mode + Networking" Before your VM gets to BIOS force Shut down. Attach RTX video Card Start "safe mode + Networking" Download and install NVIDIA drivers. Reboot

You will have to do this to every VM that you need that RTX card on. Hasta la victoria siempre

@zxcp As of right now I am assuming it is because I kill the VM shorter than normal.

@ember1205 it's not a matter of not being "well optimized" or xen arbitrarily removing support for old CPUs (we don't do that), it's a matter of the CPUs he's using being so old they're missing entire instruction sets that are required for proper virtualization. The Z800 systems you mention use xeons a full generation newer than the processors he's using, and were the first intel xeon generation to have proper full IOMMU/VT-d/etc instruction set support, so of course I'm sure they worked just great. The Z800 line is the same xeon generation as the 11th gen dells I mentioned, which is why I stated that is the oldest I would comfortably use - any generations older than these (like the poweredges zxcp is using) are missing core instruction sets xen relies upon.