LikeBot

LikeBot was the original way to get reactions in Telegram channels and still has a large audience. You write a post in the bot's private chat, choose the buttons (up to a handful of emoji), and publish the result in your channel via inline; each tap increments a counter under the post. Unlike native reactions, admins control the exact set and readers cannot add others.

It is free and official. The workflow is manual, so it suits small channels and one-off posts; for scheduled publishing with buttons look at channel assistants such as Controller Bot.