There are no restrictions in the jam rules for the content of your game jam entry. There may, however, be restrictions based on the copyright laws of your country, the IP holder or lawyers of those IP holders. If you are making content based on non-original content, please give context in the description of your game so there can be no confusion.
In terms of NSFW content, or content inappropriate for children, we haven't specifically disallowed it, but please don't give us cause to invent a new rule for GBJam10. If you do make content which may upset some players, please include a content warning as GBJam is often played by children and their parents.
This should be in its own topic, but please see the response here: https://itch.io/jam/gbjam-9/topic/1638574/only-allowed-to-use-gamepad-input