[{"details":[{"_id":ObjectId("60c84d9968c2d100154f3391"),"expiryDate":ISODate("2021-06-12T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-06-10T06:50:01.046Z")},{"_id":ObjectId("60c84d9968c2d100154f3392"),"expiryDate":ISODate("2021-06-25T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-06-16T06:50:01.046Z")},{"_id":ObjectId("60c84d9968c2d100154f3393"),"expiryDate":ISODate("2021-06-25T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-06-15T06:50:01.046Z")}]},{"_id":ObjectId("60c84d9968c2d100154f3392"),"details":[{"_id":ObjectId("60c84d9968c2d100154f3391"),"expiryDate":ISODate("2021-12-12T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-12-10T06:50:01.046Z")},{"_id":ObjectId("60c84d9968c2d100154f3392"),"expiryDate":ISODate("2021-06-25T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-12-30T06:50:01.046Z")},{"_id":ObjectId("60c84d9968c2d100154f3393"),"expiryDate":ISODate("2021-06-25T05:30:00.000Z"),"updatedAt":ISODate("2021-06-15T06:50:01.046Z"),"createdAt":ISODate("2021-12-15T06:50:01.046Z")}]}]

db.collection.aggregate([{"$addFields":{"lastCreatedAt":{$max:"$details.createdAt"}}},{"$match":{lastCreatedAt:{/** input your date range here*/$gte:ISODate("2012-06-16T06:50:01.000Z"),$lt:ISODate("2021-12-30T06:50:01.100Z")}}},{$group:{_id:null,docs:{$push:"$$ROOT"},numOfLastCreatedAt:{$sum:1}}}])