Hacker News Reader

I found Obsidian’s way of doing it to be a bit jarring at first but now that I’ve used it for awhile I personally quite like it. Just takes a little while of getting used to

You could probably do this in a way that doesn't trigger text reflow if a popover appeared with the visible syntax exactly positioned such that the extra syntax slightly obscured surrounding text. It's a tradeoff but I think that might be slicker.

Not a user of either of those but that sounds an awful lot like "Reveal Codes" from WordPerfect which saved my ass more than once when formatting got screwed up in a document.