Your question has nothing to do with the GPL. If your concern is that the code may count as derivative work of existing code then you also can't use that code in a proprietary way, under any license. But that probably only applies if the LLM regurgitated a substantial amount of copyrighted code into your codebase.

If it can’t be copyrighted, then no. Licenses rely on the copyright holder’s right to grant the license. But that would also mean it’d be essentially public domain. I’m not sure there’s really settled legal opinion on this yet. Iirc it can’t be patented.

Can you link to them?

The way the world is currently working is code created by someone (using AI) is being dealt with as if it was authored by that someone. This is across companies and FOSS. I think it's going to settle with this pattern.