Hello Ahmad,
Thank you for your message.
Could you please clarify if you have the
Monitor Driver installed on the remote Host machine? It's required to be installed in order for the
Blank the Host's screen feature to work properly.
If you're not sure about the monitor driver, you can double-check if the driver is displayed in the Windows device list:

If the driver is not installed on the remote Host machine yet, you can install it performing the following:
1. Open
Settings for Host and navigate to the
Driver tab.
2. Select
Install:

3. Restart Host.
You can install the monitor driver during the Host installation as well by selecting the corresponding checkbox on the
Installations Options step:

Hope that helps.