This is of course assuming you take AI-generated code unchanged. But you don't, in my experience. And that generates a new work fully copyrightable even if the original wasn't. Just like how the fad a decade or so ago of taking Tolstoy and Jane Austen works and adding new elements -- "Android Karenina" and "Sense and Sensibility and Sea Monsters" are copyrighted works even if the majority of the text in them was from…
That's not how copyright works. The modified version is derivative. You can't just take the Linux kernel, make some changes, and slap a new license on it.