I don't understand why you're downvoted for this question.
What's wrong with Telegram is the privacy story. It's not end-to-end encrypted, meaning that the server can read the content of your messages.
I hear that Telegram has a great UX, which makes it popular. But in terms of security... it's wanting.
To me it's just not an encrypted messaging app. I don't even get all the discussions about it...
It's a bit like if we analysed the E2EE guarantees of email over and over again. Every year, multitudes of people would publish a post explaining how email is "badly encrypted". Well, email is not E2EE, period. If you want E2EE, use a system that has E2EE.
You're again linking to old critiques of an old protocol no longer in use. Can you stop doing that, please?
Except to the protocol, which you continue to post aged posts identifying vulnerabilities that have nothing to do with the rewritten version. That is not honest presentation of the facts.
Telegram is a joke in professional cryptography circles https://x.com/matthew_d_green/status/726428912968982529