Can't run the code without opening serial monitor

hello everyone
im using protocentral-pulse-express with arduino MEGA and Nextion display (ENHANCED NX4832K035)

i setup the code to display the output of the sensor to the display and it works well
but i have to open serial monitor every time i need to display the output of the sensor

i want to add power supply and use the sensor and the display without the computer but opening the serial monitor.

this it my code

#include <Wire.h>
#include "max32664.h"

#define RESET_PIN 04
#define MFIO_PIN 02
#define RAWDATA_BUFFLEN 250

max32664 MAX32664(RESET_PIN, MFIO_PIN, RAWDATA_BUFFLEN);


void mfioInterruptHndlr(){
  //Serial.println("i");
}

void enableInterruptPin(){

  //pinMode(mfioPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(MAX32664.mfioPin), mfioInterruptHndlr, FALLING);

}

void loadAlgomodeParameters(){

  algomodeInitialiser algoParameters;
  

  algoParameters.calibValSys[0] = 120;
  algoParameters.calibValSys[1] = 122;
  algoParameters.calibValSys[2] = 125;

  algoParameters.calibValDia[0] = 80;
  algoParameters.calibValDia[1] = 81;
  algoParameters.calibValDia[2] = 82;

  algoParameters.spo2CalibCoefA = 1.5958422;
  algoParameters.spo2CalibCoefB = -34.659664;
  algoParameters.spo2CalibCoefC = 112.68987;

  MAX32664.loadAlgorithmParameters(&algoParameters);
}



void setup(){

  Serial.begin(9600);

  Wire.begin();

  loadAlgomodeParameters();

  int result = MAX32664.hubBegin();
  if (result == CMD_SUCCESS){
    Serial.println("Sensorhub begin!");
  }else{
    //stay here.
    while(1){
      Serial.println("Could not communicate with the sensor! please make proper connections");
      delay(5000);
    }
  }

  bool ret = MAX32664.startBPTcalibration();
  while(!ret){

    delay(10000);
    Serial.println("failed calib, please retsart");
    //ret = MAX32664.startBPTcalibration();
  }

  delay(1000);

  //Serial.println("start in estimation mode");
  ret = MAX32664.configAlgoInEstimationMode();
  while(!ret){

    //Serial.println("failed est mode");
    ret = MAX32664.configAlgoInEstimationMode();
    delay(10000);
  }

  //MAX32664.enableInterruptPin();
  Serial.println("Getting the device ready..");
  delay(1000);
}

void loop(){

  uint8_t num_samples = MAX32664.readSamples();

  if(num_samples){

    //Serial.print("sys = ");
    Serial.print("sys.val=");
    Serial.print(MAX32664.max32664Output.sys);
    Serial.write(0xff);                           
    Serial.write(0xff);
    Serial.write(0xff);


    //Serial.print(", dia = ");
    Serial.print("dia.val="); 
    Serial.print(MAX32664.max32664Output.dia);
    Serial.write(0xff);                           
    Serial.write(0xff);
    Serial.write(0xff);

    //Serial.print(", hr = ");
    Serial.print("hr.val="); 
    Serial.print(MAX32664.max32664Output.hr);
    Serial.write(0xff);                           
    Serial.write(0xff);
    Serial.write(0xff);


    float sop2f = float(MAX32664.max32664Output.spo2);
    //Serial.print(" spo2 = ");
    Serial.print("spo2.txt=\"");
    Serial.print(sop2f);
    Serial.print("\"");
    Serial.write(0xff);                           
    Serial.write(0xff);
    Serial.write(0xff);

  }

  delay(100);
}

Of course you can't. When the serial buffer is filled, that code just waits until there is room in the buffer.
Paul

how can i avoid it and let the code work without opening the serial monitor

The buffer will transmit and empty regardless of whether or not it is connected to anything.

I've never had a program stall due to lack of the serial monitor.

I suggest you start deleting the MAX32664 stuff until you can run without the serial monitor.

Or you can start with a simple program that prints to serial, verify it works without the monitor then start to add in the MAX code.

Or start with one of the MAX example programs then add in some serial prints.