There’s no way OpenAI is letting Apple use them for free. So where is the money coming from? AI is the hot new thing and expensive to operate so I imagine Apple is paying quite a lot. There needs to be a new form of income or this wouldn’t make sense from a business perspective. I image there is data harvesting from the AI service.
You can. For instance, look up the Brave Search extension on Firefox. Or you can just set the brave.search link to your home page button on any browser.