Apple could still retain the capability to delete malicious apps from phones (even apps that weren't installed via the App Store).

Presumably Belarus would then make a demand that Apple delete Telegram from people's phones as it is "malicious", but I'd hope that forcing a company to delete things from someone's phone is legally harder than forcing them to hide things on their own servers.

And that capability would be trivial for Belarus to side-step.

Presumably you're imagining some sort of cat-and-mouse game where Belarus release a new version of the app, and then Apple add that app to the blacklist (which iPhones would update daily from Apple's servers, and broadcast via AirDrop).

Rather than blacklisting the app's name or hash, Apple would probably have to blacklist the Developer ID, which it would be hard for Belarus to generate quicker than Apple could blacklist.

Unnecessary because they can already force you to pass all monetary transactions through an app like WeChat and can track you all they want there.

And let's not pretend that Apple has shown any willingness to stand up to the Chinese government.