technically, Telegram does support end to end encryption but it's not activated by default, so every discussion is saved in clear text on servers accessible by Russian authorities.
When you activate the encryption, you have to forego basic features like push notifications, it's made ever so slightly less useful to make you not really want it.
Signal on the other hand is fully encrypted by default and run by a non-profit organization. Their code is open source and can be audited.
Telegram's official documentation tells their unpaid volunteer workers to discourage people from using E2EE: https://tsf.telegram.org/manuals/e2ee-simple
I really don't understand them why - as far as I read - why it became the defacto app for CP. It's a great thing for the authorities to have achieved. Bravo.
So on the push notification thing -- If you get push notifications without using a third party push notification server, Apple and Google log the notifications and police can issue warrants for them. So IF for any reason you use Signal, make sure the contents of the message are turned off for Push Notifications.
The notification that goes through the Push server is empty. It simply tells Signal to check its own server. G and A don't see the message content at all.
good call!
telegram is russian. i dont trust russian.
https://www.securemessagingapps.com/
This is a decent resource on some technical differences, however I don't know how up to date it is
There may have been further changes after the arrest last summer