There used to be an entire subreddit that basically did this. There were hundreds of fake users each posting and commenting. No real users were allowed to post or comment. I loved it because they would sort of mirror what was currently on the front page but in much more ridiculous way.
Edit: It was called subreddit simulator. And the creator said it used Markov chains. So no need to use bad prompted LLMs. Just do it the “old fashioned” chatbot way.