Evil (Emacs 27.1) produced this:

  {
  "squadName": "Super hero squad",
  "homeTown": "Metro City",
  "formed": 2016,
  "secretBase": "Super tower",
  "active": true,
  "members": [
          {
          "name": "Molecule Man",
          "age": 29,
          "secretIdentity": "Dan Jukes",
          "powers": [
                 "Radiation resistance",
                 "Turning tiny",
                 "Radiation blast"
                 ]
          },
          {
          "name": "Madame Uppercut",
          "age": 39,
          "secretIdentity": "Jane Wilson",
          "powers": [
                 "Million tonne punch",
                 "Damage resistance",
                 "Superhuman reflexes"
                 ]
          },
          {
          "name": "Eternal Flame",
          "age": 1000000,
          "secretIdentity": "Unknown",
          "powers": [
                 "Immortality",
                 "Heat Immunity",
                 "Inferno",
                 "Teleportation",
                 "Interdimensional travel"
                 ]
              }
          ]
  }

Interestingly, the first-level items are not indented. Real VIM 8.1 produced the same format, but the first-level items _are_ indented.