ADHD

food for thought, feel free to totally toss away and ignore

Personally I don't recommend finding some random simple notes app because you will likely use it for awhile, run up into a limitation and eventually abandon it.

I recommend you invest your time in a software or system that can grow and shrink with the amount of spoons/degree of hyperfocus you have to spare on the system. It should be brutally simple to open a note and start writing and not make you feel like haphazardly tossing a couple of bullet points onto a page is using the tool wrong (like a barely used planner with weeks and weeks of empty days staring you down with shame).

On the other hand ideally it should be capable of expanding along any direction your mind wants to go without shackling you to a system that won't satisfy whatever ridiculous and capricious bullshit system you come up with whenever your hyperfocus-eye-of-sauron turns for a brief but glorious hot second onto the topic of organizing yourself. Your tool needs to be able to instantaneously fold up from a gargantuan all encompassing idea processing machine to a glorified digital post it note in the snap of a finger, otherwise if you are like me than you will just abandon the byzantine complexity of it whenever you go through an "organizational winter" (and you will never stick with a more limited tool in the first place).

I also recommend you to try to find a tool that is open source, organizational tools are too long lived and vital to be entrusted in the whims of whatever company gobbles up the company that originally made your organizational app of choice.... that maybe you accidentally balanced your ability to live a functional life on somehow when you weren't paying attention....

I recommend:

Joplin https://joplinapp.org/

Logseq https://logseq.com/

I recommend these tools because you can trust that you can develop a long term relationship with them (HABITS), that you can have control over the details of so you can tweak something to fit your needs if you really need to (if you are like me and hate organizing yourself, the smallest detail in an app can ruin it like a menu bar that I can't get out of the way and hide when I am focusing) and that your system and associated habits will never be lost, locked up in a proprietary data format/app that becomes abandoned when the company goes out of business. Learn to use Joplin or Logseq as a dumb simple notetaking app, keep your use of it extremely straightforward and simple and then as the years go by if you feel like it, learn little by little how broader uses of the tools are possible and let them slot naturally into your life.

That is just my advice though!

(edit I use emacs org-mode which is like these but I wouldn't call it simple necessarily, but I wouldn't hesitate to use joplin or logseq as an alternative they are both mature tools with deep functionality that also let you use them like a simple dumb notepad to jot ideas down in)