Or does it refer to public channels only?
No, not yet.
> Or does it refer to public channels only?
On Telegram channels and groups are not E2EE. I'd assume that's were most of the crap is spread.
Having said that I am no fan of installing law enforcement inside private companies. However, telegrams noncompliance with court orders is problematic particularly related to protecting human rights of 3rd parties in the digital age.
You can get a warrant (a court order) to open a piece of mail, and the USPS isn't going to refuse to hand it over.
[technically they could, but someone would get stuck with contempt of court charges]