[{"_id":"5fc4c13f32ab3174acb08540","userId":"go05111","folders":[{"_id":"5fb7b0473fddab615456b166","folderTitle":"first-go"},{"_id":"5fb7b0473fddab615456b16b","folderTitle":"second-go"}]}]

db.collection.aggregate({$match:{"folders._id":"5fb7b0473fddab615456b166"}},{$project:{folders:{$filter:{input:"$folders",as:"f",cond:{$eq:["$$f.folderTitle","first-go"]}}},_id:0}})