It's probably a bad idea to use GenAI artwork to represent your site or instance or project.
If you've used a search engine recently, you'll know how difficult it is to get proper human-written information because it is buried in slop. People will assume your site/instance/project is slop too if it uses GenAI art.
If you can't afford to pay an artist, there are lots of creative commons-licensed media sites such as https://commons.wikimedia.org which let you use free human-made art and images.