I just wanted to add that NoMachine doesn’t set or add anything to your Linux environment. Anything related to your profile, a service or system setting, e.g. the screensaver in your case, doesn’t change because you installed NoMachine. So the fact your screensaver was activating itself after a very short time is not a bug of NoMachine. It was simply a setting in Gnome that had been configured incorrectly 😉
Further references: https://www.nomachine.com/AR11K0074