I've noticed a pretty significant uptick in new accounts posting complete garbage. I don't mean the comments are bad, they're not even words in many cases.
I collected a few of them:
https://news.ycombinator.com/item?id=47130684
But it also seems some topics (in particular AI) attract a lot of accounts that post incredibly low quality comments, far below the quality you'd expect from HN. Ofte it's in reasonable English, but it's just inane reddit-level drivel. Unclear if these topics attract low quality posters, or if these are bot accounts.
Also looking at the three first pages of /noobcomments, we find 28 comments with EM-dashes in them. That's not proof of AI, but if you compare with /newcomments, you find exactly one EM-dash going back as far. That's a bit of a statistical aberration.