Good question. Itch already has a built in way for developers to disclose AI use. However you would first need to determine what that even means.
Which brings us to a bit of a problem in that almost every big game engine: Phaser, Pixi, Godot, and LittleJS used AI code in their development. Web browsers like Chrome and Firefox, are built using AI. Google search also uses AI. So it's really not fair to say that any game was developed completely without AI.
LittleJS also provides a set of tools specifically for people to make better games using agentic programming:
https://github.com/KilledByAPixel/LittleJS-AI
What I think what you mostly want to avoid is low effort entries that are basically AI one shots. This is usually pretty obvious from the thumbnail if not within the first 10 seconds of gameplay. Feel free to just avoid those entries or give them a bad review if you want.