There are clients on Matrix that support custom emojii, such as Sable and Commet. Neither are absolutely perfect, but I know people who daily-drive one of the other (or both, which is where I'm at depending on the device).

For the most part, now that Matrix is merging those Matrix 2.0 specs finally, and the 2.0 features are already out in the wild with excellent results, it has a really good base, and as expected we've started to see clients build more into the average-consumer space to pose as alternatives to both niche and mainstream audiences such as Discord, Whatsapp, etc - Which it just wasn't/isn't able to do on Matrix 1.x (legacy).