If all parties agree, yes. But that likely is not the case - e.g., an app developer would likely want to have maximum freedom in what data they send over the wire, while a user would want to minimize the amount of data transmitted (for simple cost reasons) and also control which personal and/or sensitive information is transmitted.

Encryption where the user does not control either of the endpoints stacks the odds in favor of developers and against users.

I agree however, that the situation for the web (e.g. everything that lives inside a browser) is still pretty good thanks to the ability to add custom root CAs and general user the browser's debugging and inspection tools.

However, if you try to find out what exactly a mobile app, a game console or an IoT device is doing, you soon find yourself out of luck even if you're the owner of those things.