As far as I know, everything iCloud and Apple Intelligence runs off of their own data centers if you happen to live "near" one, but you could still be using AWS and/or Google as well.

I live near the Danish Apple data center, and pretty much all my iCloud traffic goes there, with a small fraction (<10%) going to Stockholm, which has both AWS and Google data centers, so I assume they're using both for geographical redundancy (erasure coding)

It gets a bit more fuzzy once you start moving into Movies/Music/TV/Billing/whatever as well as their backend services for the store and monitoring.