From what I have seen, AI's use of the em-dash always falls into the technically correct "semicolon like" usage that is ambiguous and confusing when semicolons are also used. Most people who use em-dashes this way do it to "fix" their serial comma use and the difference is generally easy to spot and they often forget to remove the comma they meant to replace as ggm did;

> before AI emerged, -- it would be very plausible

Not criticizing ggm, posting on the internet is closer to spoken language than written with punctuation being more about replacing the lost verbal cues than structuring a carefully composed thought.