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

{
    "display": {
        "icon": "minecraft:ender_pearl",
        "title": "Enter a Gateway"
    },
    "parent": "minecraft:story/enter_the_end",
    "criteria": {
        "entered_end_gateway": {
            "trigger": "minecraft:enter_block",
            "conditions": {
                "block": "minecraft:end_gateway"
            }
        }
    }
}