Backyard Paintball

The developers describe how their game uses AI generated content like this:

This game uses AI generated content. Some 2D artwork on the store page and in the game was created using generative AI tools during development. All AI generated art was reviewed and edited by our team before being used.

Required on Steam store pages since 2024. It covers content that ships in the game, on its store page or in its marketing — Valve does not require a disclosure for AI tools used during development, so this says nothing either way about how the game was made. Check it on Steam.