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.
Because there is nobody who has signal, and everyone is using telegram. I could switch to signal, but there is nobody to chat with. Telegram users and group chat owners wouldnt switch to signal, because they dont care, and nobody else in chat does so. So unless telegram will be legally banned by government, nobody is going to do anything about using it.