I like to use more uncommon tools (it often bites me afterward but it’s funnier this way
I know the feeling.
How about this: https://docs.xcp-ng.org/installation/install-xcp-ng/#9-networking
Try setting a static ip address on xcp-ng itself, during the install phase. (this was how devices got onto networks before dhcp). You'll have to make sure it doesn't conflict with anything else on the network.