Further, there have been constant references, in articles from very reliable, reputable sources (see: CNN, NYT, FOX, etc.) since Russia's invasion into Ukraine about Russia's use of Telegram. I don't know that I could count the number of times I've seen phrases akin to, "based on conversations between Russian military commanders on Telegram," used as a source. The issue is that Russia's military essentially sucked at setting up their own communications channels, so they fell back to Telegram.
Even Politico and the WSJ can confirm...
https://www.politico.eu/article/telegram-ceo-arrest-pavel-du...
https://www.wsj.com/world/russia/russia-military-telegram-fo...