I heavily suspect that it's overdiagnosed in the US, but heavily underdiagnosed in the EU.

I have adult ADHD, and even though I tried to get help when I was turning 20 and started to fail university (I had an average of 1.3 for the classes that I did finnish, I just couldn't commit to anything) it took me 3 years until I got a diagnosis (due to ridiculously long waiting times for doctors appointments).

In the end I only got a doctors appointment because I got diagnosed with multiple sclerosis, and my neurologist, who is also a psychyatrist was like "btw I also think you have ADHD, ever tried to get help for that?".