[{"sections":[{name:"section1",fields:[{fieldName:"Author",fieldValue:"John"},{fieldName:"Movie",fieldValue:"Avenger"}]}]},{"sections":[{name:"section1",fields:[{fieldName:"Author",fieldValue:"Hengry"},{fieldName:"Movie",fieldValue:"Test"}]}]}]

db.collection.aggregate([{"$addFields":{"sortField":{"$reduce":{"input":"$sections","initialValue":null,"in":{"$reduce":{"input":"$$this.fields","initialValue":null,"in":{"$cond":{"if":{$eq:["$$this.fieldName","Author"]},"then":"$$this.fieldValue","else":"$$value"}}}}}}}},{$sort:{sortField:1}},{"$project":{sortField:false}}])