@wangling @scoop @ursala7
Let's begin by saying that supplements are another form of medication- any time you introduce a substance beyond what your diet provides or your body manufactures, you are medicating yourself.

As a medicine, a supplement can be beneficial, harmful or neutral.

Supplements can also interact with each other, or with other medicines you take, whether prescription or over the counter.

All medicines and supplements must be evaluated based on whether the benefits of using them outweigh any risks.

What about studies and reviews? Some are scientifically sound and provide solid information. Many are commissioned by someone "with skin in the game" and a goal of proving or disproving a particular point. Overall, most are poorly designed and/or executed - too few participants, not having a control group, not accounting for differences between people, poor followup...

So, how do we use the info? Google Scholar (scholar.google.com) allows you to look specifically for reviews of published studies/papers on topics of your choice within a specific time frame. Using that tool to read the summary, then possibly do a deeper dive into individual studies (citations are included.)
Phew! If you're still here you begin to understand why it takes so long to find good answers. At this point AI is NOT a shortcut in this process, because you have to read every source they cite to see if it meets the criteria for being a good study.

If you can cite the exact study from Lung Matters, I will look at it - the studies I found were either regarding nasal cilia, not lungs, or dated back to 1987.

Now it's time to take this discussion back to the topic at hand NAC supplements. Some people here find it helpful for thinning and/or reducing mucus. In early days of my journey I tried it and thought it helped a bit. But I am always in the "less is better" camp so stopped it to see what happened - I detected no difference so I no longer use it.