I didn't know Nix had support for embedded systems. Where are the images defined?
$ my-arm-system = nixpkgs.lib.nixosSystem { system = "aarch64-linux"; modules = [ ./configuration.nix ]; };
$ :b arm-system.config.system.build.images.iso
nixos-rebuild build-vm (--flake DIR#HOSTNAME / configuration.nix)
./result/bin/SCRIPT
to build and launch a nixos vm with qemu.
build-vm is the same as building the configs “config.system.build.vm” attribute.
nixos-rebuild is fine for getting started but you end up needing to use the attribute path to do anything more complicated like CI caching or inspecting the drvPath.