I'm sure there are flakes that can do that, but I just use the config file, adding things as I find I need them. Flakes weren't really all that well documented when I first installed it so I never messed around with them. Out of box though, it was fairly decent for relatively simple needs. If I remember correctly, the graphical install could set you up with any of a half dozen different DEs out of the box.

One heads up. While NixOS is a Linux distribution, it is radically different design philosophy from every other Linux distribution I've ever used. In some ways better and far easier to setup and maintain, and sometimes, as headache inducing as Gentoo or Arch. Once you have it setup to your liking, though, it has proven incredibly solid and hard to break.

Here's a redacted copy of my configuration.nix file. I really need to clean it up, reorganize, and remove things I'm not using anymore, but it's what I'm running on my desktop. Basically hasn't changed since KDE6 came out something like a year ago. I think the last change I made after that was when I finally added flatpak support.

https://pastebin.com/8G7Hv4y2