Another good open source, markdown based alternative that I used for a long time is Joplin. Also has git sync built in and is cross platform.
Interestingly, GitJournal has an import function from Joplin.
Import your free notes that work just as well into our paid app with the same or less features.
That's a pretty cynical view of what's happening here.
A real human is working full time on GitJournal.
They have built the mobile apps for you as a convenience. But if that's not a good fit for you, The project is open source[1]. Build it yourself.