ADHD brains are usually visual learners. Use that to your advantage.
Colour code EVERYTHING and stick to it. Consistency is everything.
For example, when I did A level history, usually it’ll ask questions about events in history and you study the different factors, is always use specific highlighters and coloured pens for specific factors: political factors (blue), social/religious factors (orange), economic factors (yellow)
Stick to those colours ALWAYS, we struggle with memory and sorting info so this makes it kind of automatic if you do it consistently enough.
As you get closer to exams, use sticky notes IN THOSE SAME COLOURS and put key info on them and stick them in places you’ll see so that your brain automatically remembers the info without putting pressure on you