Using a hardware gate/compressor vs noise reduction

Yes, computer fan noise is exactly what Noise Reduction does well. A background sound that doesn’t change.

There is a correction suite for people reading for AudioBooks. It will achieve ACX AudioBook compliance repeatedly without a compressor.

https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1

It uses some custom tools you have to install.

Is the machine a laptop? Are you reading from the screen? Print the work, move the laptop slightly to one side and put it on a towel. Put something between the laptop and the microphone. Breakfast cereal boxes with towels over them? Do Not block the laptop ventilation. You can play tricks with a directional microphone. They’re usually dead straight back. That’s where you put your noise.

Getting rid of noise before you record pays very well.

Koz