Through much trial and error I have learned that the problem is due to the ArduinoBLE.h library - which is NOT included - in the BLE_server sketch. More specifically, it is the version number of the ArduinoBLE.h library that is the problem.
If I use version ArduinoBLE 1.3.1 and not the latest version, the error vanishes.
To avoid conflicts when using an ESP32 , I have found it best to change the library properties file of the Arduino BLE library so that it is not used with the ESP32.
In the ArduinoBLE library properties file I have saved this change.
In my experience, inspite of the claimed compatibility, I think it best to use the esp library with the esp32 and the Arduino library with the other platforms.
There is a file named BLEDevice.h which is part of the ArduinoBLE library as well as the ESP32 BLE Arduino library. It is getting used by the compiler.
Is this the 'esp library' you were referring to?
I'm not certain what you mean. In the esp 32 core for Arduino there is a included library called BLE.
So I'm not certain what functionality that 'dummy.h' library contains.
I am using is an ESP32 microcontroller. Posting to the NANO33 forum was a mistake as noted earlier.
This odyssey began by trying to figure out how to wake a ESP32 board from deep sleep with BLE - which I now believe is not possible - thus my opening the ESP32 BLE Arduino / BLE_server example sketch because a server sketch example does not exist in the Examples / ESP32 folder.