Telegram has some nice client software and services, but I wouldn't use it if I were you.
"The default messages and media use client-server encryption during transit. This data is also encrypted at rest, but can be accessed by Telegram developers, who hold the encryption keys."
Not OP, but Signal is a pretty good choice in my experience. Giving a "general overview" for them is tough, but the best I can think of is "Telegram-looking, Telegram-experience, but using the Signal Protocol, which is considered **a** gold standard. Centralized servers off-shore (I think). And no bots."
Alternatively, I've heard good things about Matrix/Riot. Federated, very much like Mastodon. Personally I couldn't use it because the iOS and Android apps are just "not there."
Some information on both is available on Privacytools, including other alternatives. :D
@jksn I've been using Riot a little bit. It's not Slack, comparatively slow.
I get a lot of ghost content on riot.im pages when components change--it isn't very smooth. Everything feels like I'm clicking on eggshells hoping to avoid clicking on something else when the page decides to update.
A Mastodon instance for info/cyber security-minded people.