Keep the OS. Change the setup.
You do not need a spare laptop to see whether Nix is useful to you. Begin with the environment you already have.
On an existing Linux distribution
Use Nix alongside the distribution’s package manager. Let the host continue to manage the operating system while Nix provides selected tools or development environments.
Check the official installer’s requirements for your distribution and security configuration rather than pasting a command intended for another setup.
Upstream references (1)
On macOS
Nix provides packages and development environments on supported Macs. Package availability can differ from Linux.
For declarative management of supported macOS settings and services, look at nix-darwin. It does not replace the macOS kernel or turn a Mac into NixOS.
Upstream references (2)
In a Linux virtual machine
Run NixOS in a VM when you want to try the full operating system without replacing the host. Hardware integration will differ from a bare-metal installation.
Upstream references (1)
In CI and container workflows
Use Nix in a compatible build environment and deliver the output your deployment expects: a package, an image or another build result.
Upstream references (2)
Other routes, maintained by their own communities
NixOS-WSL adapts NixOS for Windows Subsystem for Linux. Nix-on-Droid offers a Nix environment on Android; it is not a complete NixOS phone operating system, and its repository describes it as prototype-grade.
Treat these as separate projects with their own support boundaries.