I am mostly frustrated because I enjoy using em dashes in my writing and don't want to have to stop using them because people will assume my content is AI-generated.
https://www.chicagomanualofstyle.org/qanda/data/faq/topics/H...
https://www.tomsguide.com/how-to/how-to-type-an-em-dash-on-w...
https://en.wikipedia.org/wiki/Hyphen
It uses the full em dash (—) whereas humans usually use the en dash (-), because it's actually on your keyboard.
It's as simple as that. It doesn't prove something was written by ChatGPT, but it's a useful heuristic.
If you want to humanize your text, sprinkle in some artificial spacing errors. Group the em dash with the preceding character sometimes. Occasionally switch between the british and american versions of words.