This is a red herring, and entirely irrelevant
The question of whether or not humans or AI "do" create new ideas is not relevant
The question is whether or not humans or AI can create new ideas
Humans quite obviously can, because humans did. Even if you see the same common themes for 10000 years, at some point those themes were created by humans. We must be capable of creating new ideas, even if we don't actually do it very much.
AI may not even be capable of creating new ideas. It probably isn't in its current state, and may not ever be