Running the XenClean.exe utility that ships with xcpng-winpv-9.1.146.0-Release-x64, on a Windows Server 2022 VM (Version 21H2 - OS Build 20348.5020) with Citrix Guest Tools v9.4.2 installed, results in the following error and a subsequent BSOD with stopcode = INACCESSIBLE_BOOT_DEVICE:

• [Alert] Cleanup FAILED: -2147467259 Msiexec failed with code 1605
• [Interactive] Cleanup task status is Error

Also, contrary to what's stated in the release notes, the VM does not automatically reboot. I suspect that's a consequence of the utility not completing successfully to trigger the reboot.

ULTIMATE SOLUTION FOR ME (might be different for you) :

• Mount any Windows ISO to the VM (I used the Windows Server 2022 ISO)
• Navigate to the Advanced tab of the VM and change the boot order so DVD-Drive is first (don't forget to click Save)
• Press any key, as prompted, to trigger a boot into the ISO
• Press next and select "Repair your computer"
• On the next screen select "Troubleshoot" and then "Command Prompt"
• You will now have a command prompt open and at the X:\ drive
• Type C:\ and hit enter to drop to the system drive for the installed OS
• Navigate to the folder holding the XenBootFix utility. For me it was C:\Users<MyUser>\Downloads\xcpng-winpv-9.1.146.0-Release-x64\package\XenBootFix
• Type XenBootFixe.exe C:\Windows and wait for the utility to finish, then reboot the VM.
• Install the XCP-ng Windows Guest Tools and reboot when prompted.
• After the VM boots back into Windows, confirm on the VM's General Tab that you see the message Management agent 9.1.145-77 detected.
• Don't forget to go back into the VM's Advanced tab and disable the DVD-Drive under Boot Order.

Sharing this, in hopes that the Vates team will see and address this issue, and it might help someone else out of a jam.