从集合[Mongodb]中获取N条最新的不同记录

Question

const eventSchema = new Schema({
  id: Schema.Types.ObjectId,
  serviceName: String,
  event: {
    type: { type: String, required: true },
    subType: { type: String, required: true },
  },
  properties: Object,
  created_at: { type: Date, default: Date.now() },
})

上面是Event模型的架构。我怎么能得到日期为type的最新N个不重复记录（由subType和created_at分开）？

样本数据：