I just found this article published in 2020 about the possibility of an increased risk for knee osteoarthritis from taking oral NAC: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7418329/#:~:text=NAC%20users%20had%20a%20significantly,users%20than%20among%20NAC%20nonusers.
The cause of the correlation is not known. (Perhaps those who take NAC, e.g. for lung issues, also have a greater propensity for developing arthritis.)
These results conflict with the following study (wich is why I suggested that the correlation cause might not be straight-forward.): https://nutritionreview.org/2018/09/nac-reduces-joint-damage-prevents-osteoarthritis-in-mouse-study/

I take a curcumin with black pepper capsule twice a day, do daily stretching routine, use Voltaren gel and an anti-inflammatory essential oils rub and do deep breathing with visualization. If I get a really bad flare, I use 20 mg prednisone for 2-4 weeks. And I see my PT several times a year for 6 week tune-ups that include a lot of manual therapy.

I tried NAC and found it flared my arthritis. You may want to discontinue for a few days or a week and see, if it helps. I am using collagen daily and it has helped my arthritis. I found, if I run out of collagen and do not use it for a week, my hand joints start to be uncomfortable. We are all different and react differently to different drugs and supplements. Best wishes in finding what works best for you!