I’m not that into organising “stuff” into folders or compartments. I don’t do it more than I have to digitally or analogue. The reason I never do it is that what I am going to look for when I need it is almost always different from what I would have categorised it as. My approach is instead to organise things based on what it is. All my plain text notes are in the same place, all my pictures are in the same place; all my Field Notes are in on place and all my larger notebooks in another.
I use search to find my stuff on my computer, and I almost always find it. The way I do it with my notebook is that I write when I started using a notebook, and when I completed it on the first page. Then I write a date on the top of each “text” or “list” or whatever. Then I write “(posted)”, “(transcribed)” and so on on the bottom of each text if I have done so.
It isn’t perfect, and it can be cumbersome to find stuff sometimes. But it gives me just enough context to find what I am looking for.
And I can look through all of my notebooks many more times before I even get close to the time it would have taken to set up and maintain a good system for categorising all of my used notebooks.