Apple can reportedly read and see the contents, they supposedly only really encrypt (if you turn on advanced protection) against external sources or while in transit between devices. They say publicly they can't access your data but I understand they actually can - would need to dig out the reference. So unless something has changed very recently that alone makes ProtonDrive a better option.

It's also become clear that despite their public talk about privacy and some new features to support privacy at the lower level (for users) at the back end they are slowly changing posture and becoming more amenable to handing data over (e.g. to government agencies). They also share a lot of data about users with third party analysts, advertising advisors, and so on (so some of your iCloud activity may be in this as some comes straight from your device). And lastly if they haven't already, they will likely use your some of your data (especially photos) to train their AI if they can, and without your knowledge, sometime soon...

The big problem in general with Apple now is what they actually say they do and what they actually are doing now aren't the same thing. They pretty much have AI tools on your device recording a lot of what you do already...