[{"sku":1,"values":[{"x":false,"z":100}]},{"sku":1,"values":[{"z":100}]},{"sku":2,"values":[{"x":false,"z":100}]}]

db.collection.aggregate([{$group:{_id:"$sku",count:{$sum:1},values:{$push:"$values"}}},{$addFields:{values:{$reduce:{input:"$values",initialValue:[],in:{$concatArrays:["$$value","$$this"]}}}}},{$project:{_id:0,sku:"$_id",values:{$filter:{input:"$values",cond:{$or:[{$eq:["$count",1]},{$ne:["$$this.x",false]}]}}}}}])