I don’t use iCloud for sharing anything, even photos. I just keep my personal documents and files. I suppose those are protected from any Apple use...
I'm no lawyer, but I can speak to the technical side of things; I am a computer science student having done extensive research on Apple's security techniques specifically.
If you do not use share functions on iCloud Drive, and your data is only in your 'private' iCloud Drive, the data is encrypted with a combination of your AppleID and device specific tokens (Generated when accepted through 2-factor authentication). Apple may technically own your data in a lawful sense to operate its service, but in the encrypted state, Apple cannot access the data themselves; Only the encrypted variant. The system is very much designed around the concept that "We can't be forced to give your data away, because we can't even see it ourselves". Now, I'm not saying it's perfect; Holes in the encryption algorithm could be found or the AppleID/Token combination used to encrypt your data could feasibly be weak enough that brute-force attacks could be feasible; But that's very unlikely with the salted key hashing performed and the use of long tokens.
Also, this is as of now kinda region specific. As you may have heard Chinese law requires that Apple uses a different strategy for data stored there; And if I recall correctly, Apple outsources iCloud in that region - I am not sure how the encryption scheme is handled there; If it is still encrypted the same way but just stored on outsourced servers (although even then the encryption would be slightly weaker, since Apple also uses server-side hardware encryption keys to; on top of data-encryption, enforce firmware locking) or if maybe Chinese law also has some clauses preventing that. - I believe there was also similar goings on in Russia.