renewable-resources/data/renewable/recipe/elytra.json

{
  "type": "minecraft:crafting_shaped",
  "category": "misc",
  "pattern": [
    "M M",
    "MDM",
    "M M"
  ],
  "key": {
    "M": "minecraft:phantom_membrane",
    "D": "minecraft:diamond"
  },
  "result": {
    "id": "minecraft:elytra",
    "count": 1
  }
}