After upgrading the Arduino IDE to the newest version (1.8.19) on Windows 10, I could not get anymore the port menu to show the network port for the YUN.
After much research on the Web and many unsuccesful trials to solve this rather nagging problem, I came accross a post by Zygbaja which provides a solution for communicating with the ESP8266 NodeMCU board in OTA Mode.
I can attest that Zygbaja's solution also works for the YUN board or the Dragino YUN shield.
The trick is to disable the Internet Protocol IPv6 in the network properties. For the process of disabling IPv6 in Windows 10, see for instance Process of disabling IPv6 in Windows 10.
Note : using the IDE to communicate (for sketch uploading or monitoring) is only possible if the YUN board is on the same network as your PC (also, I changed my network settings from public to private).