When the client window is in fullscreen mode, using the Control + Alt + M keystroke (or the Minimize toolbar button) minimizes the window to the taskbar/Dock.

On macOS this is no longer working as expected, as the SDK used in NoMachine 8 doesn't allow a frameless window to be minimized.

Implementing the fullscreen through Spaces will better integrate with macOS and remove the need of minimizing a window to access the underneath area.