Syncing E2EE chats across devices is more difficult to pull off, but it’s definitely possible and other services do that by default.
That’s because if you are able to get your private key on another device, then Google, Apple or Microsoft, and that means anyone, also have access to your private key. And you don’t have e2ee, literally.
I would look into how Matrix handles this, for example. It involves unique device keys, device verification from a trusted device, and cross-signing. It’s not just some private key that’s spread around to random new devices where you lose track of.
That’s because if you are able to get your private key on another device, then Google, Apple or Microsoft, and that means anyone, also have access to your private key. And you don’t have e2ee, literally.
I would look into how Matrix handles this, for example. It involves unique device keys, device verification from a trusted device, and cross-signing. It’s not just some private key that’s spread around to random new devices where you lose track of.