squashfs -> ext4, which makes images ~5x larger. :(

[nixos-qemu-vm-isolation] / flake.lock

{
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1686960236,
        "narHash": "sha256-AYCC9rXNLpUWzD9hm+askOfpliLEC9kwAo7ITJc4HIw=",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "04af42f3b31dba0ef742d254456dc4c14eedac86",
        "type": "github"
      },
      "original": {
        "owner": "NixOS",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs"
      }
    }
  },
  "root": "root",
  "version": 7
}