The problem is that people misunderstand the security model in Telegram, and believe that it's e2ee. Except that most features are not, only secret chats are e2ee, and people mostly don't use those (because the whole point of Telegram is the nice group features).
IIRC audio and video calls are E2EE as well (in addition, the four emoji that appear on a call allows both parties to check that no one is eavesdropping)
