#define LED_PIN 21
#define BUTTON_PIN 33

byte buttonState;
volatile byte buttonReleased = false;
byte LEDState;

void IRAM_ATTR buttonReleasedInterrupt() {
  // ISR triggered byt BUTTON_PIN FALLING
  buttonReleased = true;
}

void toggleLED() {
  if (LEDState == LOW) {
    LEDState = HIGH;
  } else {
    LEDState = LOW;
  }
  digitalWrite(LED_PIN, LEDState);
}

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT);
  LEDState = LOW;
  pinMode(LED_PIN, OUTPUT);

  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN),
     buttonReleasedInterrupt,
     FALLING);
}

void loop() {
  if (buttonReleased) {
    buttonReleased = false;  // reset the state variable
    toggleLED();             // process the action
  }
}