OctopusLupid

I think Matrix would be a good fit. It strongly encourages E2EE and is federated like email.

Chromebook in the early days? I’m not sure if it’s open even now (without dual booting Linux).

Facebook has been pretty vocal about iOS privacy restrictions as well. They don’t need to make their own store on Android; but they very well might on iOS.

Others don’t have the same needs you do.

You don't speak for most people.