Obsidian has a quick shortcut to switch between view mode and edit mode, end their edit mode is actually partially formatted (# headers are displayed in a bigger font)

> Not to mention handling the various differences between Markdown flavors

Funnily enough, I was looking for Python markdown to HTML rendering library, and the author of one of the biggest two closed a bug on me reporting a minor incompatibility saying "that is GitHub format, we don't support it, we only support CommonMark, GitHub format is non-standard and broken".