[{_id:0,cars:[{name:"vw polo",door:3},{name:"vw golf",door:5}],possible_colors:[["black","blue"],["white"]]}]

db.collection.aggregate([{$addFields:{cars:{$map:{input:{$zip:{inputs:["$cars","$possible_colors"]}},in:{$mergeObjects:[{$arrayElemAt:["$$this",0]},{possible_colors:{$arrayElemAt:["$$this",1]}}]}}}}}])