The forum doesn't even need any specific rule to cover using ChatGPT or any other AI chatbot, the rule on plagiarism should cover that because when you use ChatGPT to reply to posts, or to make posts on this forum, you are basically not writing anything from your head/knowledge, but basically copying and pasting. The only thing here is that it is somewhat difficult to prove beyond reasonable doubt that a user is using ChatGPT chatbot.