I know that shitty AI bot all too well. Unfortunately I've tried and failed to get people to leave as well. I have a community of ~20k users. Sad reality is that not only does no one care but they will actively attack you for even suggesting such a thing.
Facebook knows what they're doing. The only way to close the group is to remove each and every member, one by one, and even if you actually wanted to spend the time actually doing that (I have), they will "detect automated activity" and lock your account.
I created my own private Lemmy community. Even set up Photon as a frontend. Not 1 single user joined.
So yeah, we're so fucked.