In order to create NoMachine GNOME virtual desktops, it's therefore necessary to install the Mesa 3D graphics libraries for supporting the accelerated graphics of the desktop. 

If the Mesa libraries are not installed, the NoMachine virtual desktop fails to start.

System logs report a message like:
Sep 28 13:47:15 fedora28.host gnome-session-binary[3996]:
WARNING: software acceleration check failed: Child process exited with code 1

and NoMachine server log reports:
Creation of virtual session in NoMachine user interface ends with: 'The session negotiation failed. Error: Session failed, application terminated prematurely.'
 

There are two possible alternative solutions:
1. Using a lightweight desktop environment which doesn't require 3D effects instead than GNOME 3.
2. Installing the Mesa libraries for using GNOME 3.
 

First solution
Install a lightweight desktop environment like MATE or Xfce. Some examples are available here: https://www.nomachine.com/AR04K00667
         

Second solution
Install the Mesa libraries.

1. Check if both packages "mesa-libGL" and  "libglvnd-glx" are installed:

  rpm -qa mesa-libGL libglvnd-glx

2. If mesa-libGL is not installed, please install it:

  dnf install mesa-libGL

3. Check if files or symlinks "libGLX_indirect.so.0"  and "libGLX_mesa.so.0" exist:

  ls -l /usr/lib64/libGLX_indirect.so.0 /usr/lib64/libGLX_mesa.so.0

4. If libGLX_indirect.so.0 doesn't exist, create the symlink to libGLX_mesa.so.0:

  ln -s /usr/lib64/libGLX_mesa.so.0 /usr/lib64/libGLX_indirect.so.0

5. Try to create a new NoMachine virtual desktop to verify if the problem is solved.