This is different than my understanding of Google and Apple. Could you provide links to sources showing what Apple collects about its users?

Yes

Darwin. Their BSD and the foundation of MacOS and therefore all the current OSes they produce.

Your computer generates two keys. One to encrypt a message. One to decrypt the message. The encrypt key is public. The decrypt key is private. Your computer shares the public key with YouTube. The private key is never shared.

YouTube does the same thing for your computer.

Your computer will have YouTube’s public key and your computer’s private key…

Your computer will be able to encrypt messages to send to YouTube that only YouTube will be able to decrypt. Even your computer will not be able to decrypt these messages after it has encrypted them using YouTube’s public key.

Since the decryption keys are never shared they can’t be snooped. That is why it is only possible for an attacker to encrypt new messages but not read any messages from either sender.