If you are in a country that cencors Telegram or if you are connecting from a private network that requires a proxy, you can use Tor to run Telegram.
Install the Tor package
Use the commands below to install the tor package on your computer.
on Arch Linux:
sudo pacman -S tor
on Ubuntu:
sudo apt-get install tor
Start the Tor service
After installing the tor package, you should start the tor.service:
sudo systemctl start tor.service
This will start the tor service and you will be able to use it on port 9050.
Add your custom proxy to Telegram
Open the Telegram Desktop app and go to the Settings > Advanced > Connection type. Check the box that says "Try connecting through IPv6". Also click on the "Use custom proxy" selection.
Now you can add a Tor proxy. Click the ADD PROXY button. SOCKS5 should be selected in the opened window. In the Socket address section, set the Hostname to 127.0.0.1 and the Port to 9050.
That's all. Click the Save and Telegram will try to connect via this proxy.
To make this step faster, you can use this link as an alternative:
https://t.me/socks?server=127.0.0.1&port=9050
Tor by itself is not all you need to maintain your anonymity. There are several major pitfalls to watch out for (see: Want Tor To Really Work?).