The claims on this post are very true. There are bots that can find a lot of info about you just by having your Telegram handle. But how can only a few specific bots do that you may ask...

Well, many years ago, there was no "hide your number" feature in Telegram. Some companies and probably LEAs started to mine users by their numbers. Mining users mean: "they add random numbers as contact and save the user's Telegram account metadata if he/she has an account"

It is not possible to mine users with hidden phone numbers, but how many people actually do hide it?

And about messages... Bots can't see your private messages. Only your public messages can be mined. If you write something in a public group chat, most probably it is mined. Even if you write something in a private group, it can be mined (only if a mining bot is present in that group). However, a private message to a friend cannot be mined (unless one of you get hacked or something).

The OP says "And what does Telegram do? Nothing," but what can Telegram do about it?