I use a flashcard app and make question and answer cards for different things I found interesting. I mostly use it for new vocabulary though. You can use Anki which is free, or Readwise which is paid and not as good of a tool for power reviewers.

I also have been starting to post my book notes on my blog because well, because one of the books I read called “Show Your Work!” By Austin Kleon kind of encouraged me to do this type of thing. The other guy in the comments said second brain and Zettelkasten, but to keep it simple for you, that type of system is basically a precursor step to help you to posting your own notes, articles, and books, or YouTube video.

So at the end of the day you can do two things:

1. Make a question set on your notes and review them regularly.
2. Show your notes on the internet in some form. Maybe someone else will find your notes useful.

Edit: sorry for any typos. I was typing in a rush.