Hi. Maybe usefull or not.
On my XCP-ng [8.2] host i already got an RTL8125 2.5Gb network adapter running, The second nic in the host.
I do not know exactly how i got it running, but involved this forum and some console action. It was detected 'side-289-eth1' this was months ago in february i think. My first try with XCP-ng.

last week updated XCP-ng on my host en rebooted.
Now it seems to have been detected again and setup as eth1.
But 'side-289-eth1' is also still there. Same mac-address
No UTP plugged in at the moment.
Maybe just for my host, but perhaps behaviour that others encounter?