Apple is definitely using Nvidia hardware.

That was for training. For inference, they reportedly use their own silicon.

There was a rumor that emerged a few weeks ago that they broke down and made an order from nvidia:

https://finance.yahoo.com/news/apple-might-ai-game-1-1951003...

Before that, in a Wired article from 10 years ago about siri and ai, one of the apple higher ups was quoted bragging about having one of the baddest gpu farms around (paraphrasing)