Hi mivang078,
Blanking remote screen during connection is a feature that will be implemented soon. In the meantime, you have the possibility to start a separate X server (Xvfb) and attaching to it, instead of X display connected to monitor.
The article “How to use NoMachine 4 on a headless Linux server” (here: https://www.nomachine.com/AR10K00710) will give you some tips about Xvfb.
In your case, you will have to start it on display other then :0, and adjust DisplayDefault key in node.cfg.
Best regards,
Bilbotine