Ukrainians are some of the bravest people I know.
To the extent that you can, do not use Telegram. Telegram is owned by a single person. This man is a fucking liar.
Telegram infrastructure is linked to the FSB.
https://www.occrp.org/en/investigation/telegram-the-fsb-and-the-man-in-the-middle
Signal is more secure and owned by a nonprofit. The founder of Signal is a professional cryptographer.
https://en.wikipedia.org/wiki/Moxie_Marlinspike
Signal delivers end-to-end encryption by default and collects almost no data.
It’s a lot easier to get a telegram account. I use telegram for its API and automated notifications, not impossible to do that with signal, but difficult to the point of serious impracticality. Telegram groups also don’t really have anything that compares with Signal.
For person to person communication, its signal every time though.