> My issue with all notetaking applications is that all of my notes are "very sensitive data" to me. I treat my notes repository like a combination diary, scratchpad [...]

Same here. I'm currently using Joplin (https://joplinapp.org/) for note taking, which syncs my notes via WebDAV to a server under my control. Supports markdown, but if I want to publish certain notes, I have to manually transfer them to the website.