Or does it refer to public channels only?
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]
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.