From a brief overview of the source code and protocols, telegram seems alright.

The communications protocol used is pretty legti: https://core.telegram.org/mtproto

Didn't see any central auth server type business when looking through how it's setup. Happy to hear from someone with more experience.

Telegram is quite good for privacy, but it is operated by a Russian company.

The protocol is invented by the guys, so it is not to be trusted completely, but it seems to be ok

Telegram is quite popular for people from my country (Germany) for example when they are banned on other platforms like Anti-vaxx people and so on.

It's not ent-to-end encrypted. And their backend is proprietary. So you can't trust it.

It seems to work for public communication though.

Use Matrix and Element, better yet, start your own matrix server. Telegram is public and you have to use your phone number to register.