All of them were too complex, and not lightweight, cross-compatible, private/secure, or futureproof enough.
I decided to settle on the default MacOS editor using a mix of .txt/.rtf files, with extensive folder organization and the built-in tagging system. I plan on consolidating journal entries into subject categories.
Example: let’s say I learn something about investing. I write something brief about it in my \journal folder, tag it under investing, then maybe save a .pdf of the source to my \investing\temp folder.
Next, I add the new info to a note under the relevant category, such as \investing\ETFs.txt
Or, I create a new .txt/.rtf (depending my needs)
I believe tags are saved as metadata, so it should be cross-compatible.
For books, I’ll structure it as \library\broad_category \book_name\chapter_n.txt, add the relevant folder tag, and maybe add an alias/shortcut in the relevant folder. I summarize key points under relevant files such as \investing\ETFs.txt
This seems like the best method to me, but I’m open to other strategies.