> Didn't a court in the US declare that AI generated content cannot be copyrighted?

No, my understanding is that AI generated content can't be copyrighted by the AI. A human can still copyright it, however.

It's obvious that a computer program cannot have copyright because is not a person, whether legal or natural.

Whether a person can claim copyright of the output of a computer program is generally understood as depending on whether there was sufficient creative effort from said person, and it doesn't really matter whether the program is Photoshop or ChatGPT.