X11 is mostly finished. There’s still active development ongoing for eg. the hardened version of Xorg Xenocara (by OpenBSD, also used by Hyperbola GNU/Linux-libre), and the suckless mobile UI sxmo (last commit 18 hours ago https://sr.ht/~mil/Sxmo/).
Edit: also it’s fairly ironic you’re calling it dead on HN. Official Arc (the language HN’s written in) hasn’t been updated in about 12 years IIUC. xorg-server was updated last December https://lists.x.org/archives/xorg-announce/2020-December/003....