Yes, I agree with you. The author made the point about LLM's facilitating plagiarism not me.
My point is, if that is his argument, then copying is the same thing (which is ridiculous of course).
The plagiarism argument is not necessarily directed at the user of the browser. Ask yourself who is doing the publishing? And how would you cite the output of an LLM if you did publish the output?
I could ask the same for the copy function, don't see how this would ever be an issue?
Typically I'd cite to whatever it was I copied. I've never seen any kind of writing that sourced to the copy function. Have you?
And you can cite the LLM you've used, no different to citing a quote by a person.
And to answer your other question of how,
There's plenty of documentation on that directly from the source (openai, etc.) and elsewhere.