pumpkin-java-multiversion/assets/datapacks/26_3/data/minecraft/recipe/shulker_box.json

{
  "type": "minecraft:crafting_shaped",
  "key": {
    "#": "minecraft:chest",
    "-": "minecraft:shulker_shell"
  },
  "pattern": [
    "-",
    "#",
    "-"
  ],
  "result": {
    "id": "minecraft:shulker_box"
  }
}