This has already also been implied in the US. Courts upheld the Copyright Office's stance on human creation in the context of AI image generation. There's no reason to expect something that fundamental to copyright to be any different for other media, such as source code.

It's reasonable to expect this to hold for all Berne Convention countries.

All licenses are unenforceable if you don't hold the copyright, since you don't have a copyright to license. And attempting to do so would probably be perjury.

Yes. Also CC is complicated in EU. A creator can not "give up" their copy right. Work can not put to "Public Domain" as creator.

IANAL, but yes, I'd assume the license is unenforceable on the AI content.