This user has had an account on a number of Stack Exchange sites for many years, and wrote a small number of questions and answers in that time. In the last few days, they've started posting dozens of answers per day across many SE sites, and they're joining more sites every day.
I think these answers are AI-generated because
Many show telltale signs of it (others are ambiguous).
Until recently their bio said "At the moment I am studying C# to implement some ideas in AI and internet communication." After I mentioned that in a couple of comments on answers of theirs, they rewrote it; now it says they're an "amateur provocateur", and the tone in general is mocking.
They recently commented "I am just trying to help people to see the damage new policies led to. We wouldn't have this if not for moderator's strike!" and "It's all for greater good. Of course it'll be banned, but that's the price to make them address the problem sooner" (both on this answer which is now deleted). I should add that I don't really believe they have altruistic motives, since they also write mocking comments in a style similar to their current bio, and things like "you should also spend time on your development instead of this pointless gpt witch-hunt. Time is precious, my friend". It seems more like 4chan-style trolling.
My question is not "what should be done about this", but what I should do, as someone who wants this to stop but has no special powers.
In normal times I would flag the most egregious answer on each site and let moderators deal with it, but these aren't normal times.
I can downvote each offending answer once on some sites they've joined, and zero times on others, but I feel like it does little good. There's an endless stream of new answers, I don't have much reputation to spend on some of the sites, and if I'm not careful I might get dinged for serial downvoting.
I could write comments or site-meta posts or chat messages on as many sites as possible to encourage others to join in the downvoting, but I'd rather not, partly because it would be a lot of work, but also because I'd feel somewhat unsafe being their most active enemy – though perhaps that's irrational.
I have been hoping for the last couple of days that someone else would do something about it, but that doesn't seem to be happening. There aren't any downvotes at all on many of the answers.
Obviously writing this question on Meta counts as doing something, but I don't think problems like this should be handled by writing one Meta question per problem user.