[{student:"a",package:[{name:"one",createdAt:"2021-10-12T00:00:00",active:true},{name:"two",createdAt:"2021-10-13T00:00:00",active:false},{name:"three",createdAt:"2021-10-14T00:00:00",active:false}]},{student:"b",package:[{name:"one",createdAt:"2021-10-16T00:00:00",active:true},{name:"two",createdAt:"2021-10-17T00:00:00",active:false},{name:"three",createdAt:"2021-10-18T00:00:00",active:false}]},{student:"c",package:[{name:"one",createdAt:"2021-10-10T00:00:00",active:true},{name:"two",createdAt:"2021-10-17T00:00:00",active:false},{name:"three",createdAt:"2021-10-18T00:00:00",active:false}]}]

db.collection.aggregate([{"$unwind":"$package"},{"$set":{"package.createdAt":{"$toDate":"$package.createdAt"}}},{"$sort":{"package.createdAt":1,"package.active":-1}},{"$group":{"_id":"$_id","student":{"$first":"$student"},"package":{"$push":"$package"}}}])