Pretty sure this is the same as every other messaging app - metadata is never protected information. The contents of the messages may be encrypted to some extent (which on Telegram they are, not end-to-end as with iMessage, but they’re not plain text), however your IP address, username, etc are subject to subpoena on any messaging platform.
It does go on sale from time to time. I picked it up on Xbox last year for 60% off if I recall correctly.