Without human authorship you cannot have a copyright. If something has no copyright protection, it is public domain.
However, the public domain is not viral. A work made with public domain elements can itself be copyrighted. However the copyright will only protect the creative expression added to the public domain work. Everyone else is free to make their own works from the public domain elements.
But…
Holders of public domain works are NOT obligated to publish or make available public domain works in their possession.
So if you use AI generation as part of your process you still have a valid copyright. Unless the audience can extract the unprotectable elements from your final product, you have the same copyright protection as a fully human produced work.
This ruling only applies to fully AI produced works. Using AI to modify a human performance to look or sound like someone else, still copyrightable. Human filming from an AI script, still copyrightable except for the script itself.
If AI makes the final output is where there’s trouble. AI’s aren’t human, their expression isn’t copyrightable. The prompt you give the AI is most likely factual rather than creative, which would make that uncopyrightable as well.
Copyright protects humans’ creative expression, and nothing else.