Database
[{"created_at":ISODate("2020-03-19T07:27:32.158Z"),},{"created_at":ISODate("2020-03-20T12:10:19.191Z"),}]
Query
db.collection.aggregate([{"$addFields":{"created_at_str":{$dateToString:{date:"$created_at",format:"%d/%m/%Y"}}}},{"$match":{"created_at_str":{$regex:"^20"}}},{"$project":{"created_at_str":0}}])