Here’s a post that popped up on Mastodon earlier today:

https://social.coop/@eb/113804992987558055

Conclusion from the linked blog post:

But, what information is really leaving your device? There is no trust me bro element. Barring some issue being found in the math or Apple’s implementation of it, for the first time the cloud is able to act as a sort of extension to your device and your data, which is an immensely exciting proposition. Apple has managed categorise photos without knowing anything about what they contain. How cool is that.