@
charlie21 not to mention Telegram is not even a social app tool, it is marketed as a private messenger.
If put it under GDPR, it will be highly doubtful the first motive of using phone number as login option in the first place.
Also as other already mentioned, it doesn't use end-to-end encryption by default, so it is a total misleading by themselves as a marketing strategy.
So yes, a kind of people like me won't be fooled by this kind of tool who claims falsely about their value.
So as many reddit user long time ago:
https://www.reddit.com/r/privacytoolsIO/comments/6r655i/telegram_isnt_safe/