minecraft-assets/data/minecraft/recipe/netherite_axe_smithing.json

{
  "type": "minecraft:smithing_transform",
  "addition": "#minecraft:netherite_tool_materials",
  "base": "minecraft:diamond_axe",
  "result": {
    "count": 1,
    "id": "minecraft:netherite_axe"
  },
  "template": "minecraft:netherite_upgrade_smithing_template"
}