Unless Apple’s proxy loads every image in all emails independently of the user opening them, it’s still possible to track when a message is viewed by having images with unique URLs for each recipient.
> Mail Privacy Protection works by hiding your IP address and loading remote content privately in the background, even when you don't open the message.
It does load all the images independently of the user opening it.
My guess is that the server will pull a copy of everything as soon as the email is received and bundle it all into an inline blob that goes to the client.
