The manifest file records the provenance of the packages that are installed in a profile managed by nix profile (experimental).

Here is an example of what the file might look like after installing zoom-us from Nixpkgs:

{
  "version": 1,
  "elements": [
    {
      "active": true,
      "attrPath": "legacyPackages.x86_64-linux.zoom-us",
      "originalUrl": "flake:nixpkgs",
      "storePaths": [
        "/nix/store/wbhg2ga8f3h87s9h5k0slxk0m81m4cxl-zoom-us-5.3.469451.0927"
      ],
      "uri": "github:NixOS/nixpkgs/13d0c311e3ae923a00f734b43fd1d35b47d8943a"
    },
    
  ]
}

Each object in the array elements denotes an installed package and has the following fields: