this is literally impossible in any case that uses a server to process unencrypted data.

Or encrypted data where keys are shared or stolen.

If a government decides that it wants some data, they can just take it and silence whoever they want along the way. If someone is given a choice between prison or lying to an App Store, they will usually pick the latter. And if people don’t cooperate with you, you can just require them to employ agents of your government to do your work for you. Or nationalize the company entirely. Or require them to design their service in an exploitable way. Or exploit the underlying infrastructure they run on.