Hi @mos99.
Are you certain it is truly communicating over the Internet? There are several distinct components of the Arduino IDE application, which must communicate with each other. They do this via TCP/IP communication. But this happens purely internally to the machine, via "localhost".
So it is expected that you will see network traffic during a compilation, as the compilation output is streamed from the Arduino CLI helper tool to the frontend of the Arduino IDE application via localhost. However, it is not expected that a compilation will result in any network traffic over the Internet.
Of course some of Arduino IDE's features do make use of the Internet, for example:
- Notifications of availability of an update to a newer version of Arduino IDE
- Downloading the new version of the IDE when you use the auto-update feature.
- Downloading the index files that provide the data used to populate Boards Manager and Library Manager.
- Downloading
- Downloading the latest versions of the firmware offered by the "Firmware Updater" feature of Arduino IDE
- Integration with your Arduino Cloud Sketchbook