Best bet is to seek a diagnosis from a qualified professional.
I am a layperson so wtf do I know but my layperson impression: DSM is the source obviously but there is a big gap between the words in the DSM and the details of how symptoms actually manifest for, in my case, ADHD. Also it is a diagnosis manual but the etiology of ADHD hasn’t been settled so there’s not like a brain scan or DNA analysis to test for it.