Telegram fixed a privacy-defeating bug in its macOS app that made it possible to access self-destructing audio and video messages long after they disappeared from secret chats. The vulnerability was discovered by security researcher Dhiraj Mishra in version 7.3 of the app, who disclosed his findings to Telegram on December 26, 2020. The issue has since been resolved in the app’s 7.4 version, released on January 29. Unlike Signal or WhatsApp, conversations on Telegram by default are not end-to-end encrypted, unless users explicitly opt to enable “secret chat”
Source: https://thehackernews.com/2021/02/secret-chat-in-telegram-left-self.html