I know what plagiarism is, and I know it's technically plagiarism, but I said it's not provable or clear plagiarism because you can't find concrete evidence for it since the content generated is only available to that specific user and no one else, so if you report it as plagiarism, you can't prove it, technically.
You can use that argument to say that you can't prove with 100% certainty that someone uses AI bot as well which would then make the rule against AI generated content useless.
As others said, plagiarism rule covers this nicely, but unfortunately mods are less leniant to ban people over that type of plagiarism (some would say for any type of plagiarism as well). At least for now.