mc_rebalance_datapack/data/mc_rebalance/recipes/shapeless/shulker_box.json

{
  "type": "minecraft:crafting_shapeless",
  "ingredients": [
    {
      "item": "minecraft:shulker_shell"
    },
    {
      "tag": "c:chests"
    },
    {
      "item": "minecraft:shulker_shell"
    }
  ],
  "result": {
    "item": "minecraft:shulker_box"
  }
}