I was diagnosed 10 years ago via a neuro-psych assessment. It wasn’t cheap but I wanted to assess for other areas of needs, such as short term memory retention. The assessment included an interview followed by several hours of structured testing.
These days, I believe there are quicker ways to test specifically for ADHD via a limited set of questions. A psychiatrist can certainly do this but most primary care physicians should also be able to as well. Depending on where you live, access to psychiatry might be limited and your primary care physician may be the one to manage your meds (if warranted) in any event. A psychologist may be able to diagnose ADHD but can’t offer medication options.
Re: learning disability/dyslexia, the neuro-psych testing can identify these issues. There may be simpler, more cost effective methods to identify these or other deficits. If you potentially need accommodations in the workplace, they may require some proof of assessment.