Apps (such as Signal) that care about end-to-end encryption do their own key management. So, Apple / Google servers only ever see ciphertext, and don't have access to the key material that's used for the encryption.
Afaik, e2e messengers don't include ciphertext with push notifications. It's an empty push to wake the client. Then the client contacts the origin to fetch the ciphertext.
Afaik, e2e messengers don't include ciphertext with push notifications. It's an empty push to wake the client. Then the client contacts the origin to fetch the ciphertext.