The exact criteria for a ban isn’t known, but it is possible to be banned. From what I’ve gathered from reading about people having been banned, it’s most likely reserved for very extreme cases, such as repeated uses attempting to ascertain dangerous information (how to build a bomb, assassinate a public figure, etc), or generate wildly inappropriate content like erotica about children.

​https://www.reddit.com/r/OpenAI/comments/101lc6d/has_anyone_been_banned_yet_from_using_chatgpt/