> … very specific …

That phrase is doing a lot of work. In the US, any writing is automatically protected by copyright. (This comment, for example.) Whether the author can claim infringement is a can of worms: legal costs, fair use … but your “very specific” phrasing makes it sound like there’s a prescription for exactly what is protected by copyright - there is not.

> Ideas are not protected by copyright.

The expression of the idea is, however. Same with facts. The fact that I live at a specific street address is not protected. My sentence construction explaining my specific street address is protected.

> The output of an LLM …

… is not protected, not matter its shape. The US Copyright Office has declared as much.