I do not know for sure if there are leaks from Telegram, but I think that Durov was pressed for enabling backdoors for CIA when he was arrested in France.

It's not like there's a registry of compromised apps in Russia that is available to public. When there were WhatsApp leaks it was widely published on Russian news channels, that's why I know about it and tell everyone to not trust WhatsApp.

But I don't closely follow every news item from the front, I know that some other apps are also considered compromised (mainly some navigation apps), but I don't know the whole list or if Telegram is being used on the front.

I guess the safest option is to not use telephone at all at war, since there are probably backdoors everywhere starting from cell modem firmware. I guess that since about middle-end of 2022 all military personnel has the same opinion and stopped using smartphones altogether or use them in flight mode with communications disabled.