Specifically: tabs, dark mode, and retention of unsaved documents. They’re apps for very different purposes, but Notepad has had some nice little updates over recent years.

So am I!

Nothing to do with the browser, FYI, just the markdown interpreter - regardless of whether your client is a web app or otherwise.

As you say, two spaces before a carriage return indicates a line break in most flavors of markdown. Two carriage returns indicates a paragraph break.