I've installed on a HP ML10 G9 server and all works fine on this server using UEFI based BIOS configuration etc.
The only issue I have found so far is when imported vmdk images using the wizard, even when I choose to set the BIOS to UEFI after the import and conversation has completed the VM won't boot. After looking at the settings for the newly created VM the BIOS is set to BIOS not UEFI.
Simple to resolve either be detaching the storage and removing/recreating the virtual machine and re-attaching the original imported storage. Or I am guessing (although haven't tried yet), using the console to set the machine type.
So possibly an issue with the Import Wizard?
I tried the shell commands to change the imported VM to UEFI, and although initially it looks fine when examining the console and seeing that the BIOS setting has updated. When trying to start the VM it won't boot due to an error. So after detaching the disk and deleting the VM I recreated a new VM using UEFI and no disk attached. Then once created I attached the original imported disk and it works fine.
Also I using VirtualBox to export a VM to OCI Format 1.0 which was setup running as UEFI, after the import into XCP it had changed the BIOS to BIOS not UEFI. So again I followed what I did above and the VM works fine.
So it does look like an issue with the Import Wizard, although it allows you the option to choose BIOS type it doesn't honour the setting and reverts to standard BIOS.