As someone with ADHD, I would encourage you to learn about it. Describing people with ADHD as 'having a hard time sitting in a classroom' is like describing people with depression as 'having a hard time laughing during movies.' ADHD is a complex neurological disorder involving general impairments to the entire executive functioning system. It shares genetic indicators and even some symptoms with autism, meaning that people with ADHD qualify as neurodiverse. It also persists your entire lifetime, as it is endemic to your brain structure (although symptoms may wax and wane over time).

For one example, my biggest impairments are definitely to a) general motivation, including non-work/school activities like reading a book I'm interested in (well-treated by medicine); general impulsivity, including emotional impulsivity and stimulation seeking behaviors (well-treated by medicine); and significant impairments to working memory (unfortunately not well-treated by medicine). The working memory is the real PITA. Studies show people with ADHD lack a specialized area of their brains for handling working memory, unlike non-ADHD people. This means that for me, my brain handles working memory tasks analogously to how blind people can learn to "see" with their tongues -- I have to marshal unrelated brain areas to try to make up the difference. (For an example of what this is like in practice, walking into a room and forgetting why I am there occurs at least a dozen times per day.) Another huge area of impact is to sleep; the vast majority (almost 90%) of adults with ADHD also qualify for a sleep disorder, usually delayed sleep phase.

As for jobs, actually one big risk tends to be having an emotional outburst at your boss or colleagues. Adults with undiagnosed ADHD usually end up developing a reputation for anger problems, as they have big difficulties controlling primal emotional responses. Another major area of challenge comes from our tendency towards substance abuse problems; many undiagnosed adults end up self-medicating via alcohol or street stimulants.

Anyways, I know this is kind of a big tangent from the OP, but I just wanted to throw that out there. I didn't get diagnosed until I was nearly 30 mainly because I was, in fact, able to sit in classrooms. I have an inattentive subtype, meaning it doesn't materialize as visible restlessness and hyperactivity as much as it does in others. Because I wasn't running around classrooms and acting out, I had to suffer in ignorance for decades.