I was talking about that with a friend some days ago, and they made an experiment, they just made the AI correct punctuation errors of a text document, no words at all which you can easily add manually, and the anti-AI system target 99% AI made, I don't know how to explain that, maybe the text was AI generated also IDK or there is a watermark in some place, a pattern or something.
Edit: you point will be that there is no way to fool the anti-AI systems running a private LLM?