NixOS is a bit different than most Linux distributions, because of a unique approach to package and configuration management. NixOS uses the NIX package manager to build everything…even the kernel. And even the entire system configuration (from fstab, users, services, firewalls, and more) is taken care of from within a single, global configuration file. This one-two punch makes NixOS very complex. In fact, many consider it on the same level as Gentoo.
In other words, NixOS is not for the faint of heart.
With NixOS 21.11, there are plenty of new features to be found, including kernel 5.10, nf_tables (in place of iptables), KDE Plasma on Wayland, PHP 8.0, Python 3.9, PostgreSQL 13, Spark 3, Bash 5.0, GNOME 41, systemd 249, Pantheon 6, Kubernetes-helm 3.7.0, OpenSSH 8.8p1, general LXD improvement,
The one piece of the puzzle that was not upgraded was Nix. Because of regressions in non-experimental behaviors, NixOS ships with Nix 2.3.16 (instead of the latest version, 2.4).
Download your copy of NixOS from the official download page and read the release notes for more information.