Telegram version 7.1 came out with a bunch of new features where one of them allows everyone to have comments under their channel posts.
It turned out that this comments feature isn't really stand alone but it is bound to discussion groups that were introduced much earlier.
How to enable comments in Telegram channel
First of all, you need a channel and you also need to link it to a discussion group. After that, native comments will appear automatically under all your posts except those created by bots.
It is also possible to disable them by unliking discussion group from the channel.
How comments work in Telegram
After user clicks on comments, he will appear in a separate comments chat where his and all other comments are visible. There it is also possible to reply to comments, send stickers links and other media. Even if the user is not a part of a discussion group, he will be able to read and post all comments related to the channel post.
At the same time, these comments will appear in the discussion group. Users in the discussion group may participate into comments discussion by replying to comments. And also, if group members simply post messages to the chat without replying, these messages won't appear in the comments chat.
If discussion group has any chat restrictions enabled (like slow mode for example), these restrictions will be applied to comments as well.
If you only received comments feature on September 30, you may want to become Telegram beta tester to be able to get its features before they are released to everyone.
Native comments is a good move by Telegram in general that is trying to implement native solutions for popular features that were implemented via bots in the past.
If comments are there now, we can also dream about having native post reactions and in-app solutions for channels monetisation. What other features are you waiting for?
Source: Telegram Blog