As someone that has a habit of maybe overusing em dashes to my detriment, often times, and just something that I try to be mindful of in general. This whole thing of assuming that it's AI generated now is a huge blow. It feels like a personal attack.

"—" has always seemed like an particularly weak/unreliable signal to me, if it makes you feel any better. Triply so in any content one would expect smart quotes or formatted lists, but even in general.

RIP anyone who had a penchant for "not just x, but y" though. It's not even a go-to wording for me and I feel the need to rewrite it any time I type it out of fear it'll sound like LLMs.