For adult diagnosis, you'd typically still need to identify several symptoms that were present in childhood, before the age of 12. For me, this was done by digging out all my old school report cards, which gave little indicators, and the expert private psychiatrist talking to my Mum to corroborate, too.
Criteria also state that symptoms should not be better explained by another psychotic or mental health disorder you are diagnosed with. So ME/CFS might
cover that..? One commenter said their recent ADHD diagnosis was dropped after an ASD (autism spectrum) diagnosis.
There's a good breakdown of the DSM-5 criteria for ADHD here, with a screening questionnaire you could use yourself to give an indicator: https://www.qandadhd.com/diagnostic-criteria
Of the two sub-types, inattentive verses hyperactive/impulsive (there's combined type too), I feel like maybe it's a fairly superficial difference in brain energy levels. How wired you naturally are. I feel like even mild hypothyroid might cover a lot of that that (or variation in the serotonin system, etc).
I was rarely ever over-energetic to the point of being noticeably problematic. More shy, retiring, tired, depressed in teens. I identified a fair bit with r/SCT
(Sluggish Cognitive Tempo), before I got my ADHD-PI diagnosis (age 30). It's a kind of foggy brain condition, though without all the PEM and other stuff that might come with ME/CFS. Not hard to imagine there's some latent neuro-inflamation there, or something. A case of ME in waiting, maybe. I certainly slid into it without any turning points around infections, events or trauma.