[{"_id":ObjectId("611a11a09500700009d09a12"),"userId":"abc","createdAt":ISODate("2021-08-14T07:22:00.535Z"),"isActive":true,"isEligible":true},{"_id":ObjectId("611a11a09500700009d09a13"),"userId":"abc","createdAt":ISODate("2021-08-15T07:20:00.535Z"),"isActive":true,"isEligible":true},{"_id":ObjectId("611a11a09500700009d09a14"),"userId":"def","createdAt":ISODate("2021-08-15T07:22:00.535Z"),"isActive":true,"isEligible":true},{"_id":ObjectId("611a11a09500700009d09a15"),"userId":"abc","createdAt":ISODate("2021-08-16T07:18:00.535Z"),"isActive":true,"isEligible":true},{"_id":ObjectId("611a11a09500700009d09a16"),"userId":"abc","createdAt":ISODate("2021-08-16T07:20:00.535Z"),"isActive":true,"isEligible":true,"newValue":true},{"_id":ObjectId("611a11a09500700009d09a17"),"userId":"def","createdAt":ISODate("2021-08-16T07:22:00.535Z"),"isActive":true,"isEligible":true}]

db.collection.aggregate([{"$match":{"createdAt":{"$gte":ISODate("2021-08-15T00:00:00.000Z")}}},{"$sort":{"createdAt":-1}},{"$group":{"_id":"$userId","data":{"$first":"$$ROOT"}}},{"$project":{"_id":"$data._id","userId":"$_id","createdAt":{"$ifNull":["$data.createdAt",null]},"isActive":{"$ifNull":["$data.isActive",null]},"isEligible":{"$ifNull":["$data.isEligible",null]},"newValue":{"$ifNull":["$data.newValue",null]}}}])