FYI, I have found out a great solution to create a very nice graphical user interface (GUI) using ESP32 (or any other micro-controller device)! The solution seems interesting to me because the entire GUI (on Android device) is created from the ESP32 side.
I am now building a simple MQTT GUI solution to try this out, but it seems one can also use USB, Bluetooth and Bluetooth LE very easily! I will try to show my end solution.
There are tutorials for Bluetooth classic and USB also.