I see these a lot, often seeded with exact copies of posts from reddit, stackoverflow, or github issues. I have not seen one that (to my knowledge) was seeded with fake content, but you absolutely could make them.

There is a subreddit called SubSimulatorGPT2 [0] where the author runs GPT2 on 130 subreddits and uploads posts from each of them. I'm subscribed to the subreddit and often get posts from there that I don't realize are fake until something small is off and I check the username.

[0] https://www.reddit.com/r/SubSimulatorGPT2/comments/btfhks/wh...