You need to change the location of the post in the telegram channels. Make it closer to the center, both in android applications and in the desktop application. Now the design of posts in channels looks very cheap. Each bubble with a message is shifted to the left for some reason, because of this, a lot of unallocated space remains on the right. There is only one author in a public channel (there is no interlocutor who will be on the right, as in chats), so the posts should be better aligned and made beautiful, like in social networks. For example, on Twitter or VK. Come to think of it, the empty space to the right of the post is only due to the share button and the scroll down button. The first one can be moved somewhere down or into a pop-up window, and the other one can simply be placed above the post. On desktop though, you can give the user a choice of 2 options. First: stretch the post to full width. The second is to leave the standard width of the post and set it to the center of the field. This is already implemented in the Notion wiki.
Another suggestion: a colored highlighter text highlighter. Possibility to choose from different colors, which will be slightly darker in the dark theme. I often use this in Notion or Word.
By the way, make it more convenient to upload a picture with a caption. Many of the channel authors I read seem unable to upload both text and image in one bubble in one post. Because of this, they first have a picture bubble, then a text bubble. It also looks very cheap and old, especially compared to other social networks like Twitter.
Well, I take this opportunity to offer you something else, but it will be strange: the ability to choose a background for each individual post or even each individual paragraph inside the message bubble (but you can darken it a little closer to the text) in order to be able to emotionally or informationally highlight each individual paragraph. I am inspired by beautiful modern website designs with their interactivity, where on the background of the text or on the side of it there can be some kind of arrow pointing to the text or a visual example of something from the text. If this cannot be implemented in ordinary posts, then you can at least make such a function in long Telegraph posts.
But the ability to insert pictures between paragraphs of text inside one bubble should be in regular posts too (not only in Telegraph). In addition, this will provide an opportunity to set a narrative in each post, or simply make the text more readable. For example, if the author wants to make text on top, and below - a bunch of pictures, like on Twitter, then he can easily do this thanks to such customization. Also, in this way it will be possible to make a preview for several external links at once, and not just for one at the very bottom of the post (again, very cheap and clumsy). Such customization is possible if you divide the text of the post into blocks, as in Notion. I would like channel authors to simply drag paragraphs up and down while creating or editing a post, inserting them between other content, just like in Notion
As for backgrounds in text bubbles, you can let Premium subscribers choose their own backgrounds for message bubbles in any public chat to make their messages stand out from the rest. If you're worried that their own pictures might cause age restriction issues, then I think it's best to give them backgrounds from their custom emoji sets, but a little blurry and darkened. If all this may seem too complicated or ugly in the end, you can simply let the authors of public channels and Premium users create their own unique sign, signature, to insert only it on the background of the bubble (somewhere closer to the bottom). This is definitely not going to be ugly. But please don't turn signatures into another NFT.