This is just a random speculation. There is no hard or even indirect evidence that Durov cooperates with FSB in any way. Even Whatsapp which belongs to Facebook is still available in Russia despite their explicit pro-Ukrainian stance.
The smaller services that go UP against the tech giants and have Russian backing, those will be cooperating with Russia. I don't know if Telegram counts as that or not, as I haven't looked into it. But they exist, and a lot of 'em are left scrambling now as the money dries up.
Every single daily thing is done via WhatsApp. The state realizes that which is why they carved an explicit (if a completely made-up) exception for it when they went after Instagram, Facebook and Meta. You don't want to inconvenience your brainwashed masses that much or they could be shaken out of their nirvana and start looking closely at what's going on.
https://www.nytimes.com/2014/12/03/technology/once-celebrate...