[{"user":1,"key1":{"priorityLevel":"p0","filled":false,"category":"Basic","fieldType":"input"},"key2":{"priorityLevel":"p1","filled":false,"category":"Basic","fieldType":"input"},"key3":{"priorityLevel":"p0","filled":false,"category":"Basic","fieldType":"input"}}]

db.collection.aggregate([{$project:{fields:{$filter:{input:{$objectToArray:"$$ROOT"},cond:{$or:[{$ne:[{$type:"$$this.v"},"object"]},{$eq:["$$this.v.priorityLevel","p0"]}]}}}}},{$replaceRoot:{newRoot:{$arrayToObject:"$fields"}}}])