[{"_id":{"$oid":"62fc99c00f5b1cb61d5f1072"},"service":"Network","date":"01/02/2022 00:32:51","childServices":[{"service":"MCT Latency","availability":99.9,},{"service":"MCT Packet Loss","availability":99.9,}]},{"_id":{"$oid":"62fc99df0f5b1cb61d5f1073"},"service":"Network","date":"02/02/2022 00:32:51","childServices":[{"service":"MCT Latency","availability":98.3,},{"service":"MCT Packet Loss","availability":99.9,}]}]

db.collection.aggregate([{$unwind:{path:"$childServices"}},{$addFields:{date:{"$toDate":"$date"}}},{$group:{_id:{month:{$month:"$date"},year:{$year:"$date"},service:"$childServices.service"},service:{$first:"$service"},childServices:{$first:"$childServices.service"},sli:{$avg:"$childServices.availability"}}},{"$group":{"_id":{month:"$_id.month",year:"$_id.year"},"childServices":{"$push":{service:"$childServices",sli:"$sli"}}}},{$sort:{"_id.month":1,"_id.year":1}}])