The bigger problem with Telegram is that it by default has insecure encryption settings (as opposed to Signal, where encrypted is the default, you need to manually activate it with Telegram + I think it's not possible to enable for all chats and clients) and to my knowledge, Telegram will outright co-operate with law enforcement agencies to just hand over unencrypted communications. I'd personally argue that's a security dark pattern - make privacy a big selling point, but then don't activate the security by default