Database
[{_id:1,"Y":3,"X":"Example","A":{"complex_obj":{}},"Abc":"something","Aza":1,"Azd":2},{_id:2,"Y":3,"a":2}]
Query
db.collection.aggregate([{$project:{data:{$objectToArray:"$$ROOT"}}},{$unwind:"$data"},{$sort:{"data.k":1}},{$group:{_id:"$_id",data:{$push:"$$ROOT.data"}}},{$replaceRoot:{newRoot:{$arrayToObject:"$data"}}},{$project:{_id:0}}])