I've been using the em-dash for years, having started doing so well before the dawn of LLMs -- needless to say the fact it is used as a telltale sign of LLM writing, doesn't gladden me one bit. Also because I value concise writing through picking correct grammatical elements -- like the em-dash.

Yep, me too. I’m annoyed that proper punctuation and even grammar have been co-opted by LLMs and now serve as a “tell.”