> What about when my notifications are showing up on my MacBook next to the phone via mirroring?

See perhaps §iMessage and §Continuity in Apple Platform Security:

* https://help.apple.com/pdf/security/en_US/apple-platform-sec...

Those notifications are transfered peer to peer (from your Phone to your computer) using Apple Wireless Direct Link. The contents are encrypted using AES-GCM.

talking totally out of my ass, but apple seems to have robust infrastructure for e2ee communication between your devices, for example it is known that location information in find my is not visible to apple. I’d be surprised if the channel to send iphone notifications to your mac wasn’t also e2ee