Good analysis! Fyi, if you want to tell apple to not store the decryption keys for your iCloud Photos, you can go into iCloud settings and enable Advanced Data

Good analysis! Fyi, if you want to tell apple to not store the decryption keys for your iCloud Photos, you can go into iCloud settings and enable Advanced Data Protection. You have to click through a number of warnings and set up recovery keys. We of course can’t prove that Apple isn’t still storing the keys, but imo they probably don’t even want to as it’s not their business model.