As a human, you can imagine the existence of a color you've never seen. However, it's greater than what you are able to perceive as a human. We can only see our slice of the spectrum. Therefore it's impossible to describe or create that color.

As far as I'm concerned, this is the same with AI.

You can imagine an AI that is smarter, bigger, more capable than humanity, but realistically we can't describe that.

We can't create something that is greater than our own limitations, the same way we can't create a color that we can't perceive.

Humanity is bound by it's own intellect, so any AI could only ever be as smart as we are.