A surprising number of people will tell you that the reason they prefer the closed-source Obsidian to Joplin is that Joplin doesn't use Markdown files as its backend format to store its notes, but rather a database file. (They are formatted with Markdown, though.) I think the concerns they often express around lock-in are overblown, but this may mean it's not what OP is looking for. I agree that the Joplin app is pretty nice, though more polished and featureful on desktop.