Well, (some) people on HN definitely used them before ChatGPT. https://www.gally.net/miscellaneous/hn-em-dash-user-leaderbo...
(And as #9 on the leaderboard, I feel the need to defend myself!)
(And as #9 on the leaderboard, I feel the need to defend myself!)
It's not that it doesn't exist in my native language, but I don't remember seeing them very often outside of print books, and I even know a couple typo nerds.
Maybe I'm totally off, and maybe it's the same as double spacing after a '.'. I had not heard of this until I was ~30 and then saw some Americans writing about it.