Adults, females and minorities are all under-diagnosed compared to the estimated 2-4% of the population with ADHD. And I'd guess that diagnosis rates are higher across the board in the USA than elsewhere - I read the other day only 1 in 1,000 adults in Scotland have been diagnosed with ADHD, at least an order of magnitude fewer than those who would benefit from it.

https://www.additudemag.com/statistics-of-adhd/