fz-survival-datapack/data/fz/advancements/game_event/on_sneak.json

{
    "parent": "fz:game_event",
    "criteria": {
        "on_sneak": {
            "trigger": "minecraft:tick",
            "conditions": {
                "player": [
                    {
                        "condition": "minecraft:reference",
                        "name": "fz:is_real_player"
                    },
                    {
                        "condition": "minecraft:entity_properties",
                        "entity": "this",
                        "predicate": {
                            "flags": {
                                "is_sneaking": true
                            }
                        }
                    }
                ]
            }
        }
    },
    "rewards": {
        "function": "fz:game_event/advancement/on_sneak"
    }
}