If it is not filterable, that is not helpful. There would need to be a slider, to show gen ai games that used below or above a threshold. And a percentage level is far too subjective.
If you generate an image and retouch it manually, how much percentage is ai and how much is human? You cannot tell by any objective criteria. It would be arbitrary. Also, would you simply guess the overal mean of all images? There might be some with 100% and others with 0%. But how important are they? I would say the cover image of a game is far more important than a random background.
Even for code, it is arbitrary nonsense. Big companies and news will say things like 30% of code is ai made. But this is meaningless. How much does the code do? How important is it? Oh, they might have counted the lines of code, but this is not a meaningful metric.
For Itch's tagging, just write a textual description of your ai usage in the game's description.
Oh, and there was and is human made slop. The mere use or non use of ai alone, does not make a project slop or non-slop. Especially for mobile games there are templates and game creator sites that make creation of slop rather easy. No ai needed.