minecraft-assets/assets/minecraft/advancements/story/brew_weakness_potion.json

{
    "display": {
        "icon": "minecraft:potion",
        "title": "Brew a Weakness Potion"
    },
    "parent": "minecraft:story/obtain_blaze_rod",
    "criteria": {
        "potion": {
            "trigger": "minecraft:brewed_potion",
            "conditions": {
                "potion": "minecraft:weakness"
            }
        }
    }
}