volatile bool pressed = false;

void onButtonPress()
{
    pressed = true;
}

void setup()
{
    Serial.begin(115200);

    pinMode(2, INPUT_PULLUP);

    attachInterrupt(
        digitalPinToInterrupt(2),
        onButtonPress,
        FALLING
    );
}

void loop()
{
    while (pressed == false)
    {
        // Wait here
    }

    Serial.println("Button pressed!");

    pressed = false;
}