GP (UK) prescribed Carbocisteine which, for some, has side effects. I've been using it with great success for a few years now.
ALSO, during exacerbation I need something to improve it so I use a percussion massager on my ribs/lungs. Lay or sit leaning forwards and get someone to use it around the lungs - be prepared (plenty of tissues) for what gets released. It does make me cough sometimes but that just helps the clearance.
Hope it helps.

Search Amazon for "percussion massager" - around £25 / 30$

I have heard about NAC but have never used it.
I use MucinexDM [that is what my Dr tells me to use, will even write a prescription for it also.] I have had a lot of luck with mullein tea also.

No I’d like to know more before I drown in mucus