Unpopular opinion: developers obsess about the format being Markdown. This is completely backwards. This is a hammer-sees-nail thing. You should care more about the UX. And that somewhere, someone wrote a parser for the file format. That's it. You don't have to understand every byte of it. It need not be readable text and it need not be version-control friendly. It should be a joy to use, be powerful, be easy to annotate images and pdfs. I bet none of the Markdown solutions do this as elegantly as OneNote or alternatives.