https://github.com/yggdrasil-network/yggdrasil-go
Officialy it's not support openrc, but having script
https://aur.archlinux.org/packages/yggdrasil-openrc/
s6 not exists
I could probably write you a PKGBUILD & s6 script; Currently we dont have that program in our repo, so we don't have the init script for it.
Update: Here is where you can find the files:
https://gitea.artixlinux.org/ndowens/packages-s6/src/branch/master/yggdrasil
Build successfully, but how to check logs for it?
It is /var/log/yggdrasil/current ; so you just view/edit it