I don't understand this em-dash crap. MS Word automatically converts dashes used for appositives into em-dashes. The world is awash with them.
It's magical / conspiracy theory thinking to believe em-dashes are somehow a perfect signal of LLM presence. There are no such watermarks. It's a mental shortcut by stupid people.
People usually didn't know how to type them in comment boxes like this - either going with a simple hyphen or doing multiple dashes LaTeX-style: ---
Few people were doing replies in Word and then copying them in.