There's a section about half way down that lists all end-to-end encrypted data (keychain, health, payment data, ...).

By implication, all other data is not end-to-end encrypted. That includes iCloud drive, photos, calendar, contacts and mail.

Also one big deal is how Apple handles key distribution. They absolutely could MitM that connection to get access to the user's keychain and the UI doesn't really give the user any feasible way to detect that Apple has added their own key instead of just the key for your other device that Apple doesn't control. It's "end to end encrypted" but if you just handwave away key distribution and leave that up to Apple, what's the point other than a marketing gimmick?

Are we reading the same support article? https://support.apple.com/en-gb/HT202303

Specifically listed as encrypted in transit and on server:

- iCloud Drive

- Photos

- Calendar

- Contacts

Only mail is not according to this support article.

Edit: I see the omission now. These things are not listed under the end-to-end section.

Yes, exactly, so that data is encrypted on the server using a key that is in Apple's possession.