Coffee consumption was actually one of the questions that I was asked when my therapist first suspected that I had ADHD. I used to drink 5+ cups per day (especially workdays) while feeling fairly little effect from it. I'm now on medication which works an order of magnitude better for managing my symptoms, and I rarely drink more than 1 cup of coffee per day.
It's also worth noting that ADHD often comes with other mental health comorbidities; in my case, it exacerbated my depression. I would often fall into a spiral of inability to focus -> feeling bad about myself for not completing work that I was generally more than capable of doing -> even less ability to focus. I still have depression, but starting on ADHD medication all-but-removed my most frequent trigger.
It's also worth noting that ADHD often comes with other mental health comorbidities; in my case, it exacerbated my depression. I would often fall into a spiral of inability to focus -> feeling bad about myself for not completing work that I was generally more than capable of doing -> even less ability to focus. I still have depression, but starting on ADHD medication all-but-removed my most frequent trigger.