This seems like a very open-ended question.
It seems like most people have answered similar to what I would:
You can provision cloud VMs with terraform/opentofu, initialize them as NixOS machines in a variety of ways (cloud-init, pre-configured images, nixos-anywhere), and update them using another set of ways (colmena, deploy-rs, etc.).
You can also host Kubernetes nodes; k3s is nice and easy to start with, but if you’re serious about KubeVirt, you may want to ditch NixOS and use KubeVirt straight from Talos Linux, and run NixOS inside guest VMs instead. Or you may want to use various hypervisors from NixOS to manage virtual machines. Another option than Incus (which I’ve heard great things aobut) is using NixOS as Dom0 in a Xen hypervisor:
After all of these options, can you clarify what you were going for?