Name of the app is kate.
It only does light formating and syntax highlight.
Are you looking specifically for markdown editor that just doesn't hide markup?
From the list you gave my understanding was that you are looking for higlight and that's +- it.
There are multiple markdown specific editors that do it like ghostwriter, retext, or even emacs with markdown-mode (iirc it does rendering without hiding markup, auto-formats tables, makes links clickable, etc.)
I tried editing my post to add this, but Pachli doesn't want to play at the moment.
Ideally I'd be able to use it to either see the raw markdown or the rendered version of whatever I'm writing, code in a dozen languages, articles, websites, legal documents, books, all of which I do pretty regularly.
The side-by-side view doesn't do it for me, I'd more likely than not have multiple windows open with different documents instead.
It should do autocomplete, syntax highlighting, bracket closing, live spell checking in a variety of languages, launch quickly, be rock solid when faced with a massive log file and allow me to add menu-items to run bash scripts that do things like calculate the time it would take me to read out the text at my normal podcast reading voice or covert weird characters into hrml-entities.