I’m pretty sure copyright office has settled that already. Inly human expression can be copyrighted:

> As described above, in many circumstances these outputs will be copyrightable in whole or in part—where AI is used as a tool, and where a human has been able to determine the expressive elements they contain. Prompts alone, however, at this stage are unlikely to satisfy those requirements.

https://www.copyright.gov/ai/Copyright-and-Artificial-Intell...

The United States Copyright office. There's a whole world outside the US.

And even then they can change their mind.

Does not hurt to backstop with an explicit license.