My wife is a professional writer and uses em dash a lot, usually as --, including in her casual messages, as it's common for her to use.
It's the formatting style of the whole thing that sounds AI to me. "Honestly" phrases really jumps out at me now, as well as the "But..." fragments. Not that they're bad, hell, I type out things that way too. But for it to be all together, it sounds AI after you've seen it a lot.
The em dash is fine here, emphasizing the final point. Although I would have probably used a comma myself for a post and not a formal manuscript.
Funny thing is, you can get AI to reduce a lot of these tells with a decent system prompt and staging of the writing process. So I'm surprised we're still seeing it a lot and it hasn't been weaned out of the latest versions.