Mandatory "don't put Signal and Telegram in the same sentence" notice. Not to be a snob, but Telegram is not "secure and private", all chats are not end-to-end encrypted by default, everything is stored on Telegram's servers with "forever-ever" retention. The end-to-end encryption is opt in, uses a dodgy encryption algorithm and has some limitations in terms of who you can contact and from what device etc.
Telegram is owned by Pavel Durov who also created the largest Russian social media platform VK, which later was overtaken by Russian state as a tool for crowd control and propaganda. Even if we assume that Pavel no longer has any ties with Russia and its "government", his biography should still raise at least some questions around whether one should trust Telegram.
And finally, Telegram seems to be going the "everything app" route lately, which makes it a one stop shop of personal communication, public channels, news, bots, stories etc. (you name it). While it is not a bad thing in objective terms, these features are not built with privacy in mind, as that would pose quite a technical challenge. This means that Telegram's privacy and security will only be sacrificed more and more to get more of the social features out of the door.
/rant over/