NixOS user here. I’ve been using Virtual Machines on NixOS without much issue so far. If you include the following options below in your configuration.nix then you should be good to go out of the box.
virtualisation.containers.enable = true;
virtualisation.podman.enable = true;
virtualisation.libvirtd.enable = true;
virtualisation.spiceUSBRedirection.enable = true;
services.spice-vdagentd.enable = true;
services.spice-webdavd.enable =true;
