unfortunately this was not my assumption, otherwise I wouldn't have made this post. Quoting his website: Although the client is made that it would be almost possible for sighted people to use it, there's no point, cause things such as gifs, video messages and other not useful things were not included to suit the screen reader users needs. Let me ask you, why would this suit the users of screen readers? Sorry if I sounded a bit harsh right there, but these things genuinely annoy me sometimes. I love that accessible clients are a thing, but the omission of video messages and gifs feels like it was done on purpose. It would be completely different had the dev stated that he plans to add it in the future. I once again apologize if this sounds like I'm criticising the developer, it's not my intention. I am hopeful for this clients' future.
if something is not included, there often might be an answer why. Some users don't imagine which technical problems are hiding beyond all your favorite software. Sometimes, it's better to strip some function than to include them but half working. And sometimes, it's more useful to invest time into other projects, than to spend enormous time on a feature which will be barely used.