[{"amount":{"$numberDecimal":"1"},"appId":3,"createdDttm":{"$date":"2023-09-15T10:17:41.350Z"},"day":15,"hour":10,"month":9,"newUser":true,"userId":"11111","year":2023},{"amount":{"$numberDecimal":"10"},"appId":3,"createdDttm":{"$date":"2023-09-15T16:17:41.350Z"},"day":15,"hour":16,"month":9,"newUser":true,"userId":"11111","year":2023},{"amount":{"$numberDecimal":"100"},"appId":7,"createdDttm":{"$date":"2023-09-16T16:00:01.135Z"},"day":16,"hour":16,"month":9,"userId":"11111","year":2023},{"amount":{"$numberDecimal":"2"},"appId":5,"createdDttm":{"$date":"2023-09-15T16:00:41.100Z"},"day":15,"hour":16,"month":9,"newUser":true,"userId":"22222","year":2023}]

db.collection.aggregate([{$match:/*** query: The query in MQL.*/{year:2023,month:9,day:15,newUser:true}},{$group:/*** _id: The id of the group.* fieldN: The first field name.*/{_id:null,distinctUserIds:{$addToSet:"$userId"}}}])