Short version: it's not in Linux, this is basically the very first step in getting it into Linux, it's still gonna be probably several months at least before it makes it into the mainline kernel, and then however long after that for it to make it into your distro's kernel.

FWIW, I think it was a little over 3 years from the first "RFC" for Wireguard until it was merged into mainline (part of that, though, is because some existing things in the kernel had to be "re-worked" first).