fz-survival-datapack/data/fz/advancements/unsneak.json

{
    "criteria": {
        "unsneak": {
            "trigger": "tick",
            "conditions": {
                "player": {
                    "type_specific": {
                        "type": "player",
                        "advancements": {
                            "fz:config/sneak": true
                        }
                    },
                    "flags": {
                        "is_sneaking": false
                    }
                }
            }
        }
    },
    "rewards": {
        "function": "fz:event/on_unsneak"
    }
}