I used to think people here didn't really use them before AI, but I actually downloaded a dataset of all comments over like a decade or so and counted the number of comments with an em dash, and it didn't actually change much around 2022-2023 like I had expected.

It's the spacing that's usually the giveaway to me, as well as the fact that it's not as common for people to use them like semicolons. They use them for parenthetical clauses more often. Any time I see them used with spaces as a general purpose conjunction, THAT'S when I think AI.

I have a very conversational way of writing partially because I do voice to text a lot, so the em dash just “feels” better to me than a semicolon typically.