It’s fairly trivial to map your NixOS config into a VM image: https://nixos.org/manual/nixos/stable/#sec-image-nixos-rebui...

An alternative is to “infect” a VM running in whatever cloud and convert it into a NixOS VM in-place: https://github.com/nix-community/nixos-anywhere

In fact, it is a common practice to use the latter to install NixOS on new machines. You start off by booting into a live USB with SSH enabled, then use nixos-anywhere to install NixOS and partition disks via disko. Here is an example I used recently to provision a new gaming desktop:

    nix run github:nix-community/nixos-anywhere -- \
      --flake .#myhost \
      --target-host [email protected] \
      --generate-hardware-config nixos-generate-config ./hosts/myhost/hardware-configuration.nix

At the end of this invocation, you end up with a NixOS machine running your config partitioned based on your disk config. My disko config in this case (ZFS pool with 1 disk vdev): https://gist.github.com/aksiksi/7fed39f17037e9ae82c043457ed2...