NAC is in the category of supplements that sound unbelievably amazing on paper, but are frequently discontinued by people trying to take it long term. Some people seem to like it, but it’s common for people to take it for a while and realize it’s causing side effects like anhedonia, apathy, minor sleep disruptions, or other subtle negative effects. Not everyone, but it’s a common outcome.
It also doesn’t quite live up to a lot of the incredible sounding papers for many conditions. It’s really common to find papers or even small trials purporting to find amazing effects from supplements that fail to replicate at scale. NAC does have some legitimate applications and is even used medically for certain conditions. I’m a little more skeptical that all of the amazing positives for every condition under the sun will hold up.