I have giant 2-foot by 3-foot PostIt Notes on the door of my closet. I keep my To Do List there. This includes activities (replace headlights in RV, make a SketchUp of the whole house) as well as conceptual ideas, (Blockchain for my medical data... how would that work?)
This way I see it every night before I go to bed, and every morning as I am getting dressed... the two times of day when my brain is most amenable to thinking about Stuff.
I don't keep notes elsewhere, for one simple reason: Writing something down actually allows your brain to stop thinking about it.
The brain-science geeks have been studying the importance of lists, to efficient brain function. Your brain wants to remember things for you, really badly, and so it will stress out when you try to keep more than 5 things in your head at once.
This is why they say the simple act of making a list, can help you clear your head, and get the brain working efficiently again, instead of spinning, constantly juggling things, and worrying that it is going to forget something you wanted it to remember.
So my giant Post-Its are my list. And I keep the rest in my head, to keep my head active on the two or three topics I am currently working on.
I find this to be HUGELY effective.
Because, when I write things down in books/notes/Evernote/GoogleKeep/etc, I close the cover, and my brain relaxes - "Whew! OK... he's not going to forget that now, so I don't have to think about it any more!" - and I am no longer actively processing the idea and coming up with solutions.
Close the book, the idea goes away.
Write the ideas on a huge list on the wall, in big, black Sharpie, then my brain sees it and keeps it active.
Works for me...