I think this is more of a style issue than one of correctness: lots of high-quality typeset output has used em dashes for parenthetical phrasing and plenty has used (spaced) en dashes. Bringhurst is a partisan for the en dash, for example, saying that "The em dash is the nineteenth-century standard, still prescribed in many editorial style books, but the em dash is too long for the best text faces." (/Elements/ version 2.5, p.80).

Of course, if we collectively shifted to the spaced en dash then LLMs would eventually follow; it's not clear to me that any simple and deliberate sign of humanity could remain exclusive given the incentives for machines to replicate it.