We attempted what you suggested following the steps and documentation.
Note that we have NoMachine Small Business Server, not Enterprise.
Upon making the changes and restarting the nxserver, we still did not get the option to see any other desktop other than the current user logging in.
Could there be another setting in the file, or something relating to security that were restrict this capability even with the proper configuration for the Virtual Desktop Settings?
Please see the attachments.
We also tried separately the Physical Desktop Settings (not shown here what we tried to that, but we enabled the appropriate settings for Physical).
We tested that by having a user physically log in, and then having a virtual user connect to the same desktop, but it did not give the option for the virtual user to see the physical desktop despite applying the proper settings in the configuration file (server.cfg).