[{"manager":"abc@email.com","year":2021,"month":"Nov"},{"manager":"abc@email.com","year":2021,"month":"Dec"},{"manager":"def@email.com","year":2022,"month":"Jan"},{"manager":"abc@email.com","year":2022,"month":"Jan"}]

db.collection.aggregate([{$match:{$or:[{year:2021,month:"Dec"},{year:2022,month:"Jan"}],manager:"abc@email.com"}},{$group:{_id:{month:"$month",year:"$year"},noOfOrders:{$count:{}},manager:{$first:"$manager"}}},{$project:{_id:0,noOfOrders:1,month:"$_id.month",year:"$_id.year",manager:"$manager"}}])