then I get lost in my own thoughts and have no idea where I am / how to recover if I make a mistake. It feels like the better I get at playing something, the more susceptible I am to completely biffing it because I got there by relying on my crutches instead of actually processing it the way (I think?) it’s supposed to be learned,

Those problems you describe are not unique to pianists with ADHD, but to everyone trying to learn piano anyway. It is like everything you trying to learn; at first, it does not make sense and does not fit and you seemingly need to learn everything at the same time.

Think about driving a car: You need to watch other people on the road, pay attention to traffic signs, pay attention to your mirrors, brake/accelerate, steer and (maybe) switch gears, all while listening to your driving instructor telling you what you are doing wrong. You try to focus on the road, but then you accidentally go too fast. Only when accelerating and slowing down becomes second nature, you can start focus on the other things and getting better at those.

Practicing piano is the same. You need to watch your posture, actually hitting the right keys but you can't look at the keys because you need to read the sheet music, not only where you are playing but also two bars ahead so you know that you gonna need to play a fmin7 in a few seconds, all while pedaling, etc.

And because the stakes are lower (no one is gonna die if you fumble your way through) you are going to invent shortcuts; everyone does this, and this is why teaching someone to play piano is so hard as well. If you focus teaching them one thing, they will suck at all the other things, etc.

Bottomline, if you want to play sheet music / classical music you will need a lot of discipline practicing, and in the beginning you may consider breaking your daily 1 hour practice session up into 4 x 15 minutes, until the mental fatigue goes away and your brain as build the neuronal connections; this takes at least a year.

But if you are "flexible" in your approach, maybe try learning just one or two keys, e.g. F major and G minor. Learn the scales for these keys, the chords and the inversions. Look up accompanying patters and chord progressions and soon you will be able to play a couple of accompanying melodies freely; then, you can look into improvising and how to recover from playing the wrong notes etc.

Good luck!

i have no advice about learning music but as far as reading things on paper/white backgrounds, it night be worth trying to change the colors of the sheet music or somehow add visual stimulation, maybe using some kind of app.

How is it going lately? I am in the same boat RE relying on muscle memory. I want to get a teacher - do you have one? I wonder what a piano teacher would say...

My Dad is undiagnosed, but we’re pretty sure. Once he got out of the initial beginners rut piano became easier for him. He also had a piano teacher twice a week then too. He has his favorite composers and his sheet music has to match his level. Also, like gardening, he says being stubborn (aka sticking with it) is the key. Sounds like you’re doing your best and are on the right track!

Just keep in mind that most of the time, the only one who will even notice you made a mistake when playing an instrument is you.