ChatGPT really isn't that good at creating code. But it can maybe help you create something very simple. I would be surprised if it's not allowed. Googling should always be allowed on any jam, and no one's stopping you from using a youtube tutorial to make your game. However if it looks like something someone else made 100 times before already, maybe it won't get that good ratings.
Idea: Make a game using a youtube tutorial and then attempt to learn to create your own graphics/textures for the game?
Choose a relatively recent tutorial, as some features in Unity have changed too much over the past years and 6 year old tutorials won't maybe work anymore.