I also quit smoking last year and remember that period: it felt like my body was "rebooting," but at the same time, it hadn't returned to normal yet. When I was looking for information, I came across https://ways2well.com/blog/smoking-and-stem-cell-therapy-how-smoking-affects-healing-and-results, which explains very clearly how smoking affects our body's ability to recover and even the results of medical procedures for tissue regeneration. It explains in detail what exactly has a negative effect on the cellular level and why, after quitting cigarettes, it takes time to give the body a chance to recover.