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

{
    "display": {
        "icon": {
            "item": "minecraft:end_stone"
        },
        "title": "The End?",
        "description": "Enter the End Portal"
    },
    "parent": "minecraft:story/follow_ender_eye",
    "criteria": {
        "entered_end_portal": {
            "trigger": "minecraft:enter_block",
            "conditions": {
                "block": "minecraft:end_portal"
            }
        }
    }
}