Personally I use loose leaf A4 pages, colored pens (massively useful!) and a padfolio with magnetic clip. When a bunch of notes are done, I'll staple them together and file them. I date stuff exactly or approximately or thematically group it. Then they go in boxed document folders (my context is insane, I work on mechanical/electrical/software/patents/random projects at the same time). Periodically, like changing countries, I scan stuff, digitize it, shred and purge.

Closed notebooks barely work because unless you're working on something highly sequential you wind up with 100 notebooks each of which have 5-15 pages used and are mostly wasted.

Occasionally, dated notes can be critical in IP litigation.