AFAIK most computer keyboards don't have em dashes. Rather than hit ALT+0151 every time, I've always just strung along two hyphens, like: -- Absolutely proper and correct use of em dashes, en dashes, and hyphens is, to me, the most obvious tell of the LLM writer. In fact, I think that you can use it to date internet writing in general. For it seems to me that real em dashes were uncommon pre-2022.
I disagree—LLMs don't use them properly. They always put a space between the words before – and after – the dashed part.
Using spaces is not wrong. Typographically, a hair space or another thinner than usual space is usually used, but in plain text a space is often preferred. Style guides vary of opinion on this, but newspapers often space them. Without a space they end up looking like elongated hyphens joining the words on both sides. That's not their function.