#define ISRpin 18
#define ledPin LED_BUILTIN
#define debounceDelay 10000UL

volatile bool flag = false;

void setup() {
  Serial.begin(9600);

  pinMode(ISRpin, INPUT_PULLUP);
  pinMode(LED_BUILTIN, OUTPUT);

  attachInterrupt(digitalPinToInterrupt(ISRpin), ISRflag, RISING);
}

void loop() {
  flagCall();
}

void ICACHE_RAM_ATTR ISRflag() {
  static volatile unsigned long lastDebounceTime = 0;
  if ((millis() - lastDebounceTime) > debounceDelay) // ISR Debounce
    flag = true;
  lastDebounceTime = millis();
}

void flagCall() {
  if (flag) {
    digitalWrite(ledPin, !digitalRead(ledPin));
    static int Counter = 0;
    Counter++;
    Serial.print("Counter: ");
    Serial.println(Counter);
    flag = false;
  }
}