Here I made a short demo movie. All of firmware is uploaded through OTA (over the air),  The case of nRF, firmware uploading is quite safe because boot loader and application are separated in memory, but the case of ESP32, the OTA code and user code are mixed up in the program and it's very, very easy to make it BRICK (lose control, turns into static object..)

Here is the way to make it brick in ESP32 OTA

void loop() {
  ArduinoOTA.handle();
  pinMode(LED, HIGH);
  delay(1000);
  pinMode(LED, LOW);
  delay(1000);
}

The function, "ArduinoOTA.handle()" must be kept in running in loop function but blinking LED (especially delay() function) will interrupt its operation. Once this code is uploaded through OTA, it will "brick" the module and we need wired firmware uploading (but in the epoxy, no way.)

The correct way is, (not the only way, just example)

void loop() {
  ArduinoOTA.handle();
  long int hoge=millis();
  if(hoge%1000==0){
  digitalWrite(LED,HIGH);
  }
  if(hoge%1500==0){
    digitalWrite(LED,LOW);
  }

Taking a time from mills() and delay() should never be used in loop function. This case ArduinoOTA.handle() keeps running and sometimes LED will switch HIGH and LOW.