Some things that I only realised post diagnosis were ADHD related:
Extreme sensitivity to and defensiveness around criticism (perceived and real, fair or otherwise), leading to frequently irrational reactions and escalations. Relatedly, strong opposition to being told what to do, or even to suggestions being made, due to perception of this as criticism.
Huge difficulty with routines. I remember being amazed when my husband told me he doesn't have to consciously remember to brush his teeth every day, it's something he just does automatically after his shower in the morning. Whereas I have to put measures in place to remind me every day (in my case an alarm on my phone), or it wouldn't happen.
Maladaptive daydreaming. Not idle ruminating or casual imagining, but deep, emotionally resonant daydreams which can feel as impactful on my mood and behaviour as real life events, with some story arcs spanning years.
All or nothing thinking, particularly relating to organisation and planning. I couldn't ever give a room a quick tidy for instance - something is only worth doing if it can be done to the best possible extent, like emptying every cupboard to clean and sort its contents, or not being able to start a work project because I don't have a perfectly new notebook.
Impulsivity, especially relating to spending. Knowingly spending what I can't afford for the dopamine thrill then feeing sick on the comedown. The act of buying something being much more thrilling than actually receiving or using the item.
Finding a new passion or project, spending all my dopamine on planning for it or buying supplies, then being totally disinterested in carrying out the project because all the joy and excitement associated with it has been expended on the planning.
'Out of sight out of mind' re friendships. I find it hard to maintain close connection with people I don't see regularly, even if I love them and cherish them, because when I'm not with people they rarely cross my mind.