Telegram is not a tool for sensitive communications, there are far better options if you don't trust some company or have serious adversaries (Signal comes to mind).

But it does aggressively surface the P2P AES256 text chat feature, it does P2P AES256 encrypt voice and video by default (unless I'm badly mistaken), it's got the cute emoji key-verification affordance in voice and video, it does aggressively surface features for allowing people to contact you or not, which is the exact opposite of what a "growth-hacker" PM would do.

How it stands up to a serious security audit is beyond my pay-grade, Moxie seems to think it's weak-ish, and again, that makes it a bad choice if you have credible adversaries.

But I've worked in privacy-hostile settings. Telegram is not privacy-hostile.