To be fair, anyone that has used Telegram for a while know that this is just a mock option to fool regulators. You can report all you want; zero action is taken. There are dozens of accounts that joined groups I'm in to spam CSAM. We've reported them, kicked/banned them from the group. Months later you can look them up and they're still there and still active. They even post CSAM in their public (visible for everyone on their profile) stories.
Absolutely not. This stuff happens in a lot of technology groups, custom ROM groups, even a small (but public) board game group got overrun with it once; multiple accounts posting dozens of CSAM videos/images in a minute after joining - kept going for a few weeks.
The amount of obviously illegal content on Telegram makes it plain that, for all intents and purposes, it is an un-moderated platform. They sporadically moderate when there's serious pressure, but for the most part do nothing.
Because we saw the same accounts pop up in other groups sometimes weeks later, so we started to keep track of the usernames after banning them. If you check their profile it's easy to see that they are active months later.
