Fair point! I am talking about when people receive Outlook emails or Word docs that contain em-dashes, then assume it came from ChatGPT. You are right: If you are typing "plain text in a box" on the Reddit website, the incidence of em-dashes should be incredibly low, unless the sub-Reddit is something about English grammar.

Follow-up question: Do any mobile phone IMEs (input method editors) auto-magically convert double dashes into em-dashes? If yes, then that might be a non-ChatGPT source of em-dashes.