I've used it extensively in English due to learning the language through a lot of older books - but I've never bothered to actually pull out the emdash, I would hope people can see that I'm not trying to subtract one sentence from the other.

Where do you think the LLMs got the emdash from? When I worked as a magazine editor we took good care to discern ndash and emdash in printing. In Germany it is a Bindestrich (which links words, hence "bind") and Gedankenstrich (this is where you have a pause in thinking and continue the sentence afterwards).

On the rare occasions I used Word to write things in the past, it would replace dashes with em-dash.

I normally use dashes when writing, never bothered myself with writing an em-dash properly otherwise.