How does synchronization work with the Syncthing client?

Question

Data synchronization

Probably, the question is put incorrectly, therefore, I will rephrase. There are two laptops connected to one Wi-Fi modem-router (where there is a SIM card and which distributes the Internet to the whole house). The Syncthing client is installed on two laptops, synchronization is stable.
Are you interested in whether this uses Internet traffic or does synchronization take place via a local network or a Wi-Fi network? If the default is external traffic, is it possible to configure synchronization so that it is not used? Thank you!

Answer 1

I'm sorry, and as far as I remember, you can't. Syncthing is like a cloud.

Answer 2

If I remember correctly, it works like a torrent. Accordingly, if it finds local peers, it downloads directly.

Answer 3

Turn off the Internet and find out whether the synchronization is successful or not.
If there is no synchronization point on the Internet, then the Internet is not used.