I also just noticed you were using the v3 testing version of clonezilla, not stable. I just tested that as well just in case and as expected it works out of the box - Clonezilla at its core is just trimmed down ubuntu or debian, and the xen PV device drivers are built directly into the kernel for both of these, so it's incredibly unlikely they would ever not be present. Screenshot from clonezilla live testing (same ISO you stated in your original post):
Thank you very much for your valuable advice. I will never run any third party application directly in xcp-ng. I meant inside a VM that will run on the xcp-ng hypervisor, like Xen Orchestra is.
So, I need to create a VM and set the correct network and then run nmap -sT -P0 -p 443 xo-domain to test the connection.