I setup and used a headless nixos box for about a year or so, it was fun to play around with but I did get tired after a while of the nix programming language. It was just too weird to figure out and google around to try and find what I needed to do sometimes. Trying to get virtualenvs of python packages, or using rbenv / bundler type installs for ruby was also just too much of a pain in the butt.

https://nixos.org/nixpkgs/manual/#sec-language-ruby

Trying to figure my way around installing ruby/python libraries just was too hard most of the time without a good amount of work that it wasn't worth it in the long run.

Guix has been on my radar to try and install and play with in-depth soon. If their installer will work with a VM without a days worth of research to work around any quirks I'm all in for checking it out.

If you want immutability with a traditional package manager, try Darch: https://godarch.com