Hello Joe,

much of what is written in this article here still applies to Telegram to my knowledge. Especially the leaking of metadata is apprehensive imho.

In addition to the linked article one additional comment was made:

"Update 8/31/2019: After publication of this article Telegram’s creators implemented several changes that are recognized by qualified cryptographers as a vast improvement to its encryption scheme. Since 2017, for example, the MTProto protocol has been recognized as IND-CCA secure.

Additionally, the story has be updated to clarify that Telegram does not use end-to-end encryption by default. Client-server communication is encrypted by default."
SRC comment

https://gizmodo.com/why-you-should-stop-using-telegram-right-now-1782557415

I have used telegram in the past but especially the leaking of metadata (when one is online, who is he talking too and so on) isn't to my liking at all!

Cheers!
Lucky