1. Disorders can be disabilities.
2. Medication and disabilities are not opposites of each other.
3. Disabilities are a spectrum, yes. If you have ADHD and don't personally want to consider yourself disabled, then fine. But don't go telling everyone that ADHD isn't a disability at all.

ADHD is literally listed as an example on the CDC page about disabilities. https://www.cdc.gov/disability-and-health/about/index.html

You seem to be misunderstanding what disability means. ADHD is recognized all over the world as a disability. It is literally a disability.

There are different degrees of disability. Just because someone can function doesn't mean they don't have a disability. You mentioned arthritis. Many people with arthritis can do most things, just with difficulty. Medication can also help them. They're still disabled.

Mate, in Germany I could even apply for a disability status. Medication doesn't magically cure you, it just helps. Some people have it so severely, that they can't function without help from someone. One of my best friends is like that. Meds help but he has high blood pressure so he can't take them. You're saying he isn't disabled? That is fucking wild man.