Well, you are not really forced to write a compositor these days as there are libraries that do all the heavy lifting for you.

Check out Louvre for example. Or Smithay if you like Rust. And if you want a bit more depth, there is wlroots of course (or the hyprland version). It is not really any harder than writing an X11 WM.

wlroots and smithay (I'm not familiar with louvre) do a lot of the difficult work for you, that most compositors will do without much variation but there's still a lot that compositor writers still have to do. It's still a significantly larger task than, for example, writing an X11 WM.

(Well, writing an X11 WM that also includes a built-in compositor is a bit more than just the WM, but I'd say still less than writing a Wayland compositor using wlroots or smithay. For example, xfwm4's compositor is around 5300 lines of C, which is... not nothing, but not crazy either.)