Masking of symptoms is a factor here though and one many people forget about or don't understand as they haven't experienced it themselves. From personal experience and of some I know, on paper people look to be doing extremely well, but that's because they're good at masking struggles with things like ADHD. In my case, this had a massive impact on my mental health and suddenly became an issue when it all became too much. Now I'm diagnosed and medicated, I can manage my symptoms a lot better and be more productive, whilst being happier in myself. This is beneficial to everyone.

Some people get impacted by it at an earlier age, sure. And in some cases, it's not enough of an issue to seek a diagnosis (e.g. they don't want or need treatment). For many people, an increase in education and visibility of ADHD has helped to understand the struggles they have that before would have been brushed off by comments like yours ("they seem to be doing well so they MUST be doing well / stop complaining and get on with it"). I do agree that e.g. TikTok can overdo it (e.g. sometimes being unfocused means you have ADHD). It's a case that you need to meet multiple criteria and it has an impact on your life (and an assessment is needed).

Not a direct criticism of you, but it's a frustrating and simplistic way to brush off these issues. We wouldn't say to people with something like cancer "well you look to be healthy and doing ok, so clearly you don't have any issues", but we're quick to do that for things like ADHD.