[{"_id":ObjectId("635f808302d5f6cb7c293298"),"key":"scientific","custom_properties":[{"namespace":"common metadata","key":"status","scope":"public","value":"To be uploaded","inherited":null},{"namespace":"common metadata","key":"version","scope":"public","value":"1.0","inherited":null},{"namespace":"common metadata","key":"start date","scope":"public","value":"1642550400000","inherited":null},]},{"_id":ObjectId("635f809d02d5f6cb7c29353c"),"key":"contracts","custom_properties":[{"namespace":"common metadata","key":"status","scope":"public","value":"To be reviewed","inherited":null},{"namespace":"common metadata","key":"version","scope":"public","value":"","inherited":null},{"namespace":"contracts","key":"expiry date","scope":"public","value":"","inherited":null},{"namespace":"common metadata","key":"start date","scope":"public","value":"","inherited":null},]},{"_id":ObjectId("635f80a002d5f6cb7c293588"),"key":"contracts","custom_properties":[{"namespace":"common metadata","key":"status","scope":"public","value":"To be uploaded","inherited":null},{"namespace":"common metadata","key":"version","scope":"public","value":"","inherited":null},]}]

db.collection.aggregate([{$group:{_id:{key:"$key",statusVal:{"$getField":{"field":"value","input":{"$arrayElemAt":[{$filter:{input:"$custom_properties",cond:{$eq:["$$this.key","status"]}}},0]},}}},sum:{$sum:1}}},{$group:{_id:"$_id.key",types:{$push:{k:"$_id.statusVal",v:"$sum"}}}},{$group:{_id:null,root:{$push:{k:"$_id",v:{"$arrayToObject":"$types"}}}}},{$replaceRoot:{newRoot:{"$arrayToObject":"$root"}}}])