I deleted my comment talking about it because it usually goes badly with the HN audience and their preconceived notions.

But I have had the hypothesis (as a layman) that growing around smokers affects the brain of a child, they self-medicate with tobacco, and the cycle continues, and it has for many generations until today when smoking is frowned upon and self-medication is no longer readily available. I don’t think smoking is the cause of all of ADHD, but we’ll eventually learn that dopamine dysfunction has a lot of different causes.

I've had similar thoughts! I grew up around a heavy smoker. My dad told me to never smoke and I never have. But I randomly tried a nicotine lozenge in my 40s and found it such a "lightbulb on" moment that I've been using pouches for a few years now and my executive functioning still feels better for it (though not as much now as in the first two years, alas).