This is a complete double-standard. Telegram messages are user-generated content. Is Apple going to start blocking websites in the Safari app? I'm sure one could find a lot worse things than doxxing by using Safari.
If China would threaten to ban iPhones, surely Apple will block websites. The difference is that governments can block websites without Apple approval. But governments can't block app content without blocking the entire AppStore, so they have to reach Apple.
Servers/databases have IP addresses that can be blocked just as easy to stop and App.