It's not "Wayland only", it's just that properly writing new display server-specific features for X11 is very hard compared to Wayland and probably not really worth the added maintenance cost.

Check out https://blog.martin-graesslin.com/blog/2018/01/kwinx11-is-fe...

I don't know about the other distros, but it's now the default on Ubuntu, which is one of the most popular.