Yes, you can opt in, but the Ring mobile app insists on generating your passphrase for you instead of letting you choose your own. Which means Ring could still perfectly well know what your passphrase is, even though it's supposed to be "private", since it's their code in their app generating it. Sorry, not buying it.
Edit: Also, at least according to HowToGeek [1], you lose some significant features if you enable E2EE.
(Edit to edit: My Ring app gives me an even more comprehensive list of features that are disabled if you enable E2EE. Since among them is Shared Users, which is how my wife and I can both see our Ring videos, I don't see how this is any kind of actual support for E2EE. Surely a significant portion of Ring's customers have more than one family member who wants to have access to the videos.)
