To be fair, I really don't see em dashes that commonly. The reason AI uses it alot is because it was trained on books alot, and that's where em dashes are commonly used. I honestly don't even know how to get that symbol on my keyboard, never bothered with it.

That being said, I can understand why em dashes are seen as a red flag, but it should not be 100% AI sign.

Another thing that sometimes triggers my spidey senses are lower and upper double quotes that you normally only get in word, but Apple made it a function and now some people just use them naturally, even tho, again, I don't know how to get them on my android or PC (never bothered to)