All major intelligence agencies are probably neck deep in these activities.
This is not true. WhatsApp is still working. They banned facebook and instagram but not whatsapp. Viber, Signal, Threema, Wire still works, too. The only blocked currently, i think, is Line.
Not saying "trust telegram", but still.
Second, Telegram not being blocked is hardly an argument. Neither are Signal, WhatsApp or YouTube for example. Are all of these also controlled by the FSB? And the general embrace of z-propagandists is likely due the fact that Telegram is extremely popular all over post-Soviet space. As far as I know, pro-Ukrainian people use Telegram just as much, and just as much as a news source.
None of this is to say that Telegram is a good choice for a reasonably secure messenger or is trustworthy at all (and [1] lists some very convincing reasons for why it is not so). But "may be run by the feds" is a strong claim, and so far it is not supported by evidence.
[1] https://www.pwnallthethings.com/p/russia-is-spying-on-telegr...
https://www.wired.com/story/the-kremlin-has-entered-the-chat...
https://euromaidanpress.com/2023/04/07/russian-fsb-has-the-k...
https://pdmnews-ru.translate.goog/25704/?_x_tr_sl=auto&_x_tr...
You may or may not trust these sources, however, even just the fact that at one point Durov was extremely afraid of being found by FSB, Telegram being the only network not blocked in Russia, and general embrace of Telegram by Russian propagandists, speaks for itself.