On iOS there's also Beorg [1], which I used briefly.
The problem that org-mode and Markdown face is that they are fairly minimal. It's common to use plugins, that aren't supported everywhere. This kills portability, which is a core "selling point".
I have seen it happen it Obsidian and Logseq - but even GitHub has a slightly altered Markdown spec.
I know what you mean, though at least today, this isn't as much of an issue for Org.
Org markup is fairly rich. Journelly is my 4th Org app on iOS. Neither has required additional syntax/plugin to cover my use-cases.
I would say maybe it's the opposite for Org. My apps implement a subset of Org features and, because its plain text, the user experience degrades fairly gracefully.
