I have an autism diagnosis, and I'm pretty sure I have ADHD as well. Literally almost everything on that chart applies to me in a substantial capacity. I've never sought a clinical diagnosis as an adult, but if I were to I'm fairly certain I would get one.

The ADHD assessments I had in school were all the stare at a screen and hit a button when a dot appears kind. I think they were expecting me to get bored and mess up, but that's the kind of task I'm good a hyper-focusing on short periods of time. One time the assessor told me I couldn't have ADHD because my average reaction time was one of the best she'd ever seen. I think that type of assessment is fundamentally flawed.

If you are able to function independently, then you probably won’t be clinically diagnosed even if you have some struggles here and there.

I disagree. I have official diagnoses for both ADHD and ASD and am mostly functional most of the time. If I earned enough, I'd be living on my own. I was diagnosed as an adult within the past few years while working nearly full time and I made it on time to each of the several appointments that went into getting that diagnosis. If what you say is true, I doubt the assessor would have been willing to give a diagnosis.