Telegram is most secure messenger, so It will be nice to have Home Assistant mini app inside Telegram, or maybe fork telegram and make home assistant telegram version, with super secure protocol
There is a Telegram integration which can be used to send messages if you want.
I used to use it, but unless you pay for a premium account you can’t stop the daily spam from random people/bots and it got way too annoying. I switched to messaging via the companion app, and although I don’t know the level of security involved, what is it specifically you’re worried about? It would be odd to send personal data, so as long as your not replying with commands to unlock your front door, what is the risk?
And I say “switched”, but I actually send duplicates to Telegram, as notifications on iPhone disappear forever once they’re read, whereas Telegram shows you the history. I just turned off notifications for Telegram.