[{"_id":"657c54befca2b6a2cdd935ba","data":{"name":"Bob","surname":"xxx","age":"20"},"header":{"data":"1702646974156"},"_class":"Prova"},{"_id":"657c54befca2b6a2cdd935bb","data":{"name":"Tom","surname":"yyy","age":"25"},"header":{"data":"1702646974156"},"_class":"Prova"}]

db.collection.aggregate([{"$set":{"dataX.member":"$data"}},{"$unset":"dataX.member.age"},{$group:{_id:null,data:{$push:"$dataX"}}},{"$project":{_id:0}}])