Apple is definitely collecting user data for advertising purposes, which to my knowledge is not something proton would be doing.

I wouldn’t agree that it’s “just as much as Apple” here.

In fact, this case shows that Proton Mail is exactly as private as advertised. The emails of the user stored on our servers could not have been shared because we don't have a access to them (due to zero-access encryption: https://proton.me/blog/zero-access-encryption). Of course, as any other legally operating company, we need to comply to local legislation, and the very little data we need to have (more in our Privacy Policy: https://proton.me/legal/privacy) will be shared if we're presented with a court order we have no legal grounds to contest. Proton doesn't provide privacy by refusing to cooperate with the law enforcement, but by not having access to the data.

On the other hand, as described in the blog above, Apple does have access to your data, and uses some of it to serve targeted ads: https://proton.me/blog/iphone-privacy.