NoMachine virtual desktop is a feature exclusive to the NoMachine Terminal Server for Linux family. In order to run a virtual desktop session on Linux, there must be a terminal server product installed on the host you want to access. We make available trial versions of all NoMachine Enterprise products. You can download the software from here: http://https://download.nomachine.com/enterprise/. To activate the software, create an account if you have not already done so, and proceed to the Enterprise > Evaluations section of the User Area to generate your 30-day trial license.

If you are connecting to a server where the free edition is installed, you will connect to the physical display of the target OS. The virtual desktop functionality is not supported.

Once authenticated to a host with virtual desktop support enabled, you will see a button '+' to let you 'Create a new  virtual desktop', or you can click on the 'New virtual desktop or custom session' link.