Sequencing LEDs using millis() funktion

Other Hardware LEDs and Multiplexing
5

I would get rid of lot of globals
define all intervals in an array
and let a state machine do the rest

something like

/*
  by noiasca
  https://forum.arduino.cc/index.php?topic=666044
*/

const uint16_t interval[] {500, 0, 500, 0, 500, 0, 100, 100};  // time to wait in each intervall

const byte ledPinA = 8;
const byte ledPinB = 9;
const byte ledPinC = 10;

//const byte ledPinA = 5;    // just for me as I'm using different pins ...
//const byte ledPinB = 6;
//const byte ledPinC = 7;

void handleLeds()
{

  static uint32_t previousMillis = 0;
  static byte state = 7;
  if (millis() - previousMillis >= interval[state])
  {
    // it's time for next state
    state++;
    state = state % 8;
    Serial.print(F("state=")); Serial.println(state);

    // act according state
    switch (state)
    {
      case 0:
        digitalWrite(ledPinA, HIGH);
        digitalWrite(ledPinB, LOW);
        digitalWrite(ledPinC, LOW);
        break;
      case 1:                              // these cases are all the same, so lets spare some lines of codes and combine the cases
      case 3:
      case 5:
      case 7:
        digitalWrite(ledPinA, LOW);
        digitalWrite(ledPinB, LOW);
        digitalWrite(ledPinC, LOW);
        break;
      case 2:
        digitalWrite(ledPinA, LOW);
        digitalWrite(ledPinB, HIGH);
        digitalWrite(ledPinC, LOW);
        break;
      case 4:
        digitalWrite(ledPinA, LOW);
        digitalWrite(ledPinB, LOW);
        digitalWrite(ledPinC, HIGH);
        break;
      case 6:
        digitalWrite(ledPinA, HIGH);
        digitalWrite(ledPinB, HIGH);
        digitalWrite(ledPinC, HIGH);
        break;
    }
    previousMillis = millis();
  }
}

void setup() {
  Serial.begin(115200);
  Serial.println(F("\nStart"));
  pinMode(ledPinA, OUTPUT);
  pinMode(ledPinB, OUTPUT);
  pinMode(ledPinC, OUTPUT);
}

void loop() {
  handleLeds();  // checks if something is todo with the LEDs
  //do other important stuff here
}