Use a timer (no delays) to randomly blink 2 LEDs.

Blink 2 LEDs Randomly with Timer

int greenLED = 11;
int orangeLED = 13;

unsigned long greenTimer = 0;
unsigned long greenInterval = 1000;   //this will get updated in loop()
bool greenLEDstate = LOW;

unsigned long orangeTimer = 0;
unsigned long orangeInterval = 1000;    //this will get updated in loop()
bool orangeLEDstate = LOW;

void setup()
{
  pinMode(greenLED, OUTPUT);
  pinMode(orangeLED, OUTPUT);
}

void loop()
{
  unsigned long timer = millis();  // read in current time
  
  if(timer - greenTimer >= greenInterval)  // if interval reached
  {
    greenTimer = timer;
    greenInterval = random(100, 1000) ;  // update interval

    if(greenLEDstate == LOW)
    {
      digitalWrite(greenLED, HIGH);
      greenLEDstate = HIGH;
    }
    else
    {
      digitalWrite(greenLED, LOW);
      greenLEDstate = LOW;
    }
  }
  
  if(timer - orangeTimer >= orangeInterval)  // if interval reached
  {
    orangeTimer = timer;
    orangeInterval = random(100, 1000);   // update interval

    if(orangeLEDstate == LOW)
    {
      digitalWrite(orangeLED, HIGH);
      orangeLEDstate = HIGH;
    }
    else
    {
      digitalWrite(orangeLED, LOW);
      orangeLEDstate = LOW;
    }
  }

}