Database

[{"_id":{"$oid":"5f7c2b6ee63ba648209754f1"},"duration":23,"country":"India","countryCode":"IN","city":"tamilnadu","date":"10/06/2020","timeStamp":"2020-10-06T08:31:42.768Z","__v":0},{"_id":{"$oid":"5f7c2b7ce63ba648209754f2"},"duration":12,"country":"India","countryCode":"IN","date":"10/06/2020","timeStamp":"2020-10-06T08:31:56.438Z","__v":0}]

Query

db.collection.aggregate([{$addFields:{timeStamp:{$toDate:"$timeStamp"}}},{$group:{_id:{$concat:[{$let:{vars:{monthsInString:["","Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]},in:{$arrayElemAt:["$$monthsInString",{$month:"$timeStamp"}]}}},"-",{$toString:{$year:"$timeStamp"}}]},count:{$sum:1}}},{$project:{_id:0,data:{$arrayToObject:[[{k:"$_id",v:"$count"}]]}}}])

Result