Correct. What anyone in an oppressive regime could do though is to make sure settings are set to "share your phone number with no one," as well as delete their own messages from the channel in their entirety after having been read 15-30 min later or whatever arbitrary time they'd like. They would do best to not use an @username or account name which could identify them. Beyond that, there's no way anyone in Belarus can do a thing besides physical violence and take an individual's or a group of people's phones.
There are also options for invite only channels ( I manage several TG channels, public and private) in which nobody can join without having been given the invite link, or added to the channel if their settings permit other users adding them to channels.