I wrote my first DevLog for one of my games and when I was editing that one, it had the default content editor with HTML settings, paragraph editor, bold, italics, etc. But now that I'm trying to write my second DevLog, the editor switched Markdown, except it isn't really Markdown because I can't get headings and paragraph separation to work properly. How do I bring back the original content editor?

You can control whether you have markdown or not where available on your account settings page: https://itch.io/user/settings