Margiknot
I suspect ADHD has always been around but first children now get a higher level of adult supervision so are less likely to get into difficult or potentially fatal situations ( so survive to pass on the adage genes) and also modern life is less suited to people with impulsiveness or difficulty sitting at a desk.
Marginot I think absolutely the opposite to you, and I write as family who can trace neurodiversity in the family backwards and forwards several generations.
I think one of the problems with ADHD now compared with the past is that children then lived a more structured life with times for getting up going to bed, eating meals - eaten as a family. The same at school, life was more organised and this gave those with ADHD an external structure they did not have internally. I was 'Fidgetty Phil who can't sit still', the classic description of ADHD children in the past and while I would be wiggling and jiggling when sitting (DH says this still describes me) I would not get out of my chair at school because I knew it would get me in to serious trouble. The same at home, Most ADHD children can see the things they do that cause problems and develop their own coping mechanisms.
The problem now is children live such unstructured lives, eating what they want, when they want it, going to bed as and when, with phones to distract and hyper concentrate them education is more informal, Life is full of distractions and distraction is one of the biggest problems when you have ADHD.
My ADHD son could not wait to get to secondary school and learn properly. ie sit in a classroom without other children talking and moving around him all the time and just listen to a teacher. He found that difficult enough, and his head was always in the clouds, but it was not as difficult as learning in a classroom with other children moving around and talking together and speaking to him.
The reason he eventually went to private school at 11 was because the Head master of our local secondary school came to talk to parents of children intending to send their children to the school and told us with pride that the teaching methods children were used to in junior school were used in the first 2 years at secondary school. We knew this would make the concentration problems worse so we sent him to a private school with more structured teaching where teachers, while not knowing about ADHD, recognised a child with concentration problems and had their solutions