Still a few Ubuntu Server stragglers here and there, but it works quite well as long as you keep your base config fairly lean and push the complexity into the containers.
Documentation tends to be either good or nonexistent depending on what you’re doing, so for anything beyond standard configuration but it can usually be pieced together from ArchWiki and the systemd docs.
All in all, powerful and repeatable (and a lot less tedious than Ansible, etc), but perhaps not super beginner-friendly once you start getting into the weeds. Ubuntu Server is just better documented and supported if you need something super quick and easy.