It is popular to show a progress bar to the user while a lengthy operation is in progress. Formare OTA upgrade is one of the lengthy operations. It may take from 5 seconds up to one minute to complete. It can make the user bored and the user concludes that the device is stopped working and do a hard reset.
OTAdrive Arduino library provides a progressbar mechanism to the developers in order to notify the user the operation is going on and how much it has been done.
You should provide a callback handler method to the library to get the progress changes.
The following video shows how to show the use an upadate progress bar while downloading OTA firmware in ESP32 or ESP8266. The code is same in both ESP32 and ESP8266 modules.