That is why effective end to end encryption is so important. It doesn't matter who is behind it. That is the whole point. No trust required.
Like, this app can ONLY send/recv e2e encrypted messages, and not log anything or talk to other apps.
Of course at that point the OS has to either provide good key management itself, or a good API so that the apps can still make things seamless while still not accessing the keys directly.. and probably other problems I haven't thought of.
[1] https://developer.apple.com/documentation/security/certifica...
1. All cryptographic keys controlled by the users.
2. Some way to confirm you are actually connected to who you think you are connected to.
3. A way to confirm that the code you are running is not leaking keys/content.