It doesn't look like it's achievable with vanilla Proxmox. I think if you really-really want declaratively for host machines, you'd need to ditch Proxmox in fa

It doesn't look like it's achievable with vanilla Proxmox. I think if you really-really want declaratively for host machines, you'd need to ditch Proxmox in favor of Incur on top of NixOS. There is also https://github.com/SaumonNet/proxmox-nixos https://github.com/SaumonNet/proxmox-nixos, but it's pretty new and therefore full of rough edges.