Database
[{_id:1,startDate:"2022-09-10T00:00:00.000+00:00",endDate:"2022-09-15T00:00:00.000+00:00",},{_id:2,startDate:"2022-01-10T00:00:00.000+00:00",endDate:"2022-02-15T00:00:00.000+00:00"},{_id:3,startDate:"2022-03-10T00:00:00.000+00:00",endDate:"2022-04-15T00:00:00.000+00:00"}]
Query
db.collection.aggregate([{"$match":{$expr:{"$eq":[{"$month":{"$dateFromString":{"dateString":"$startDate",}}},3]}}},])