The line between AI assisted and AI generated. For such a line those two would have to be on the same scale and increasing something would make it switch over from one state to the other.
For walking and running that is speed and the line is when both feet leave the ground.
What is the something that changes for AI involvement? I guess it is decision making and sample size. But it depends on the context. If a photographer takes 1000 pictures and selects 1, did he create the photo? Or was it the camera and the objects that were photographed? Does an orchestra conductor create music?
Those two are generally considered art. But if you prompt a gen AI system to make 1000 pictures after your direction and select 1, it currently is not considered art, and it is debated if it counts as creation. And the selected image will be AI generated, even if you change something, because an image is a big sample size.
For code creation you have templates and text book examples, discussion threads and existing code to copy from. Was it you, that made the code, if you copied it and modified it? If your sample size or your own deciscion making for the modification are sufficient to not violate copyright, yeah, you made it.
So, for code generation, I would put that line at the point where you let the AI do basically the game mechanics, instead of parts, like algorithms and functions. Also, you do not ask AI to give you 1000 functions and chose one. If it works, it works, if it does not, you make it work.
And for image generation, that line is shifted. If you ask an AI to draw the hands on your stick figure or you have the AI make the stick figure and correct the hands, both those big samples are AI generated.
As for the rules on Itch, if you do not have AI artworks and merely AI "assisted" code, but not large portions of AI code, I would just leave the disclosure blank for the time being, if possible. That disclosure feature has a lot of issues, both in the declaration and how the feature is useable for players. I have yet to see someone lamenting about how bad AI code games are, which makes me think, that players do not care about the code. They care about story and art works. But Itch lumps all "AI" together with their "no-ai" filter.