I think it’s totally fine to use AI for cover images
I strongly disagree.
If you use an AI cover image, your project will be perceived as AI made and you will be perceived as an AI user. If you otherwise are against using AI in the project, you should not use it for the first thing a new customer would see.
Also, the project actually will contain AI generated content, as a cover image is part of the project. This can of course be debated, and I probably would not actually classify something as AI made because of cover art alone. But if you were to package your work into a retail box to sell, that box would feature the cover image. If you put the game box on a shelf, there will be AI art looking at the customer. For that matter, it will also do so in a digital library view.