I notice there's absolutely no mention here of diet. I wonder what the correlation is between the countries that have seen the largest spike in ADHD diagnoses, and the countries with the most processed foods comprising a major part of the diet?

When my son was in 3rd grade, back in the dark ages around 1990, I discovered the Feingold diet, which eliminates certain trigger foods which vary from person to person. He was one of the roughly 25% of ADHD children who found it helpful. In fact, it made such a huge difference that his teacher commented on his changed behavior and asked me what medication he was on. When I smiled and said "none," she was incredulous. Although he still has ADHD, because that's how he's wired, changing his diet allowed him much better control over his non-neurotypical brain.