I mean you very much can copy
Chapter 1: Introducing the main character
..
Chapter 6: Introducing side character
Chapter 7: Arrival at the main story place
..
Chapter 17: The final chapter
In fact there are whole classifications of literature that identify basic storylines, tropes, structure etc. . The reason you couldn't copy the harry potter chapter titles exactly is because they contain specific titles, e.g. "the boy who lived", but "<my own catchphrase for main character>" as the first chapter title is again very, very common.
Also, the argument is about reuse/interoperability. Recipes are something you use and the naming is functional and it is important that it is similar enough. I am not aware of harry potter chapters being used like that, but if authors start talking about "The sorting hat" chapter as a term of the art , then yes you should be able to use that term. Similarly to how you can introduce a weapon in your novel without paying royalties to Chekhov.