[{_id:"628ceeae3df06d49419f0bb4",name:"John",notifications:[{_id:"someIdC",details:"abc",dateTime:"1653321321323"},{_id:"someIdD",details:"lmn",dateTime:"1653123412341"},{_id:"someIdA",details:"xyz",dateTime:"1653321337762"},{_id:"someIdB",details:"jkl",dateTime:"1653321337762"}]}]

db.collection.aggregate([{$match:{_id:"628ceeae3df06d49419f0bb4"}},{$unwind:"$notifications"},{$sort:{"notifications.dateTime":-1}},{$group:{_id:"$_id",notifications:{$push:"$notifications"}}},{"$project":{"notifications":1,"_id":0}}])