[jksflkjl3jk3]

Not being able to back up app data to another device that I own because its encrypted with a hardware-tied key that I can't access is a terrible design that plagues modern mobile devices. It's my device; I should be able to access any data on it.

There are plenty of viable security models where the app data could be securely protected from Apple or Google by using a key that I own and can use on other devices.

[nickff]

That sort of feature is dangerous, and very likely to cause at least one vulnerability. If I were running signal, I would be very reluctant to, and careful in implementing it.