I'm going to strongly disagree with you here. I'd argue the Cambridge dictionary's reference to a "person" is outdated.
So I'm going to follow a more modern definition, including verbal diarrhea made up by chatbots.
The copyright part is different, usually that's not a problem unless the copyright owner chases you down. But the chatbots themselves could very well be violating copyright laws on a massive scale. They must have used almost anything ever written as input, and I bet they didn't get permission from millions of different authors to reproduce it.
They violate it in the same way you violate it when you write here. When I say that Satoshi started bitcoin in 2009 it's not something I created, it's something I read at some point somewhere and I don't quote when I say things like this. Let alone when the thought is compounded and doesn't refer to a specific piece of data like this.
Do you ask permission to be able to write here when you write without quoting?
I don't think we can use that as an argument. How many decades or hundreds of years old is that Cambridge definition of plagiarism? It was defined at a time when there was no AI or chat bots, and it's no surprise that the definition only covers using another person's work. 'Something' couldn't plagiarize in those days. Now it can, and that something is the person who uses AI. As LoyceV said, the definition is outdated.
Moreover, according to search results, the definition for plagiarism dates back to the 1620s.
That's all well and good but neither of us is addressing the main issue here: I write a doctoral thesis, of my own authorship, without plagiarizing, and when I go to give a presentation of it the presentation is written for me by Chat GPT.
Is that plagiarism?
And let's get to the specific point of this thread, I create or acquire a business and when I want to make an OP for a forum I tell an AI to make it for me.
Is that plagiarism?