GP did not use emdash as evidence of AI but rather the verbose style with little signal/noise ratio and the typical phrases most LLMs like to use.

AI does not write well. People who write as AI are not the people writing well.

I've been using the compose key for over a decade but only recently discovered you can type compose <dash><dash><dash> to produce an em dash. Before then, I always just typed a double-dash (--) to simulate it.