Ask as many questions as you'd like! This is the place for that.

Maybe from the drug treatment? I cannot say for sure as I have not taken the big 3 cocktail. NTM alone in the lungs whether it's MAC or MAI or another variant seem to have symptoms which include productive cough, fatigue, night sweats, etc. I have not heard of it causing a rash. It's possible to have NTM in skin tissues but from what I've read here that is rare.

You might like to review this document which answers some questions about NTM but not sure about the rash question, it might be unrelated.
https://www.ntminfo.org/wp-content/uploads/2019/06/NTMSupplementalGuide.pdf