[{"_id":{"name":"xyz","Rollnumber":123},"Stats":[{"subject":"Maths","Updated":{"$date":"2020-08-23T00:00:10.000Z"}},{"Subject":"English","Updated":{"$date":"2020-08-24T00:00:20.000Z"}}]}]

db.collection.aggregate([{"$match":{"_id.name":"xyz","_id.Rollnumber":123}},{"$unwind":"$Stats"},{$addFields:{"Stats.UpdatedString":{$dateToString:{format:"%Y-%m-%d",date:"$Stats.Updated"}}}},{"$group":{"_id":{"name":"$_id.name","Rollnumber":"$_id.Rollnumber"},"Stats":{"$addToSet":"$Stats"}}},{"$match":{"Stats.UpdatedString":"2020-08-24"}},{"$project":{"Stats.UpdatedString":0}}])