通过简单地删除...daySchema问题将得到解决。

monday: {
        type: daySchema,
        default: {
            day: "Pazartesi",
        },
    },

但是，当默认值是动态的，就像代码中一样，更好的解决方案是创建一个函数，它接受默认值并返回一个模式，就像下面的代码一样。

const periodSchema = mongoose.Schema({
  hour: {
    type: String,
    default: "00:00"
  }
});

const daySchema = function (defaultDay) { 
                      return {
                          type: new mongoose.Schema({
                                      day: String,
                                      am1: periodSchema,
                                      am2: periodSchema,
                                      am3: periodSchema,
                                      pm1: periodSchema,
                                      pm2: periodSchema,
                                      pm3: periodSchema,
                                  }),
                          default: {
                              day: defaultDay
                          }
                      }
}

const programoSchema = mongoose.Schema({
    monday: daySchema("Pazartesi"),
    tuesday: daySchema(),
    wednesday: daySchema(),
    thursday: daySchema(),
    friday: daySchema(),
});

const Program = mongoose.model("programs", programoSchema);

console.log(new Program());

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