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.
That requires paying Google maps for their services. I don’t know how their running costs and budget work.
Signal have tons of money from selling proprietary licenses of the Signal code base to Meta (used by WhatsApp and Facebook Messenger), Google, and Microsoft.
All these partnerships were announced on Signal’s own blog, in case you don’t believe it.