minecraft-assets/assets/minecraft/advancements/end/find_end_city.json

{
    "display": {
        "icon": {
            "item": "minecraft:purpur_block"
        },
        "title": {
            "translate": "advancements.end.find_end_city.title"
        },
        "description": {
            "translate": "advancements.end.find_end_city.description"
        }
    },
    "parent": "minecraft:end/enter_end_gateway",
    "criteria": {
        "in_city": {
            "trigger": "minecraft:location",
            "conditions": {
                "feature": "EndCity"
            }
        }
    }
}