Personally I have been a fan of Joplin https://joplinapp.org for note taking.
It is also markdown-based with all kinds of features and is MIT licensed.
I have two portable installs in different folders - one journaling. The other for work notes. The problem is that only one instance of joplin can work at a time. So to use one, I'd have to kill the other. That is the only reason I'm looking for an alternative
Can you share notes with joplin?
Can you backup to my own webdav?
Sadly there really isn't any sharing. I mean, you could possibly do it via sharing the same sync endpoint, but there is no control to what would be seen.
I used to use Joplin with Fastmail's webdav.