It doesn't matter what Apple claim. All their software and hardware is proprietary, including of course their "cloud" computers. You have no way of verifying anything they say.
We can take them at their word: they tell us what is end-to-end encrypted, plainly.
Everything not on that list is not, and thus readable by Apple. The critical items not end-to-end encrypted being device backups, photos, notes, email.
In practice the end-to-end encryption of Apple products isn't better than regular encryption (in transit and at rest) with Apple holding the key. In what I assume is an effort to make the services more user friendly they have done away with key verification (something you see in Signal and Matrix-based chat services) that means the user has no way of verifying the parties of the chat and users have no say in how session keys are shared to parties. This makes it trivial for Apple to participate in all E2E sessions. It's no more work that just decrypting your non-E2E data.
It doesn't matter what Apple claim. All their software and hardware is proprietary, including of course their "cloud" computers. You have no way of verifying anything they say.