Thank you @olivierlambert !!!
I used your Tip, Booted a CD and got it running on XCP-ng
Note: chroot + dracut is not an option here, as dracut is not present in the OXE image.
Main issue was the disk device naming (sda → xvda).
Fix was:
Boot via Rocky rescue
Mount root partition manually
Update root=/dev/sdaX → root=/dev/xvdaX in /boot/grub2/grub.cfg
Replace all /dev/sdaX with /dev/xvdaX in /etc/fstab
After that the system boots fine.
Installation from guest tools via local guest tool iso went thru without any issues.
Network config is managed by OXE itself, so changes must be done via OXE CLI (not persistent via Linux/nmcli), but this will be done by the admin of OXE and that's not me.
So far it run's. We will do further testing and update this post if issues occur, in case someone else is searching for this.
Fingers crossed there will be none.
Again many thanks for pointing me in the right direction and the very quick response.
