Database
[{"totalPrice":1,"createdAt":ISODate("2020-12-25T10:56:44.798+00:00")},{"totalPrice":2,"createdAt":ISODate("2020-12-25T10:56:44.798+00:00")},{"totalPrice":1,"createdAt":ISODate("2020-12-26T10:56:44.798+00:00")},{"totalPrice":1,"createdAt":ISODate("2020-11-26T10:56:44.798+00:00")},{"totalPrice":1,"createdAt":ISODate("2020-01-26T10:56:44.798+00:00")}]
Query
db.collection.aggregate([{"$set":{"date":{"$week":"$createdAt"}}},{"$match":{"date":51}},{"$set":{"date":{"$dateToString":{"format":"%Y-%m-%d","date":"$createdAt"}}}},{"$group":{"_id":"$date","orders":{"$sum":1}}},{"$project":{"date":"$_id","orders":1,"_id":0}}])