Question marks in my serial monitor

I know it is a beginner’s code but I don’t know why my serial monitor just prints question marks, (???)
instead of the seconds

void setup() {
 Serial.begin (115200);
 TCCR1A = 0;
 TCCR1B = 0;
 TCCR1B |= (1 << CS10 );
 TIMSK1 |= (1 << TOIE1);

}
ISR (TIMER1_OVF_vect){
Serial.println (millis());
}

void loop() {
  

}

Mismatching baud rates. 115200 in the sketch and 9600 at the monitor. They have to be the same value.