is run on specified Wi-Fi networks more secure than on mobile data?

I thought that running syncthing was very secure regardless of the network on mobile data or any non public WiFi?

Anyway I don’t connect my devices (laptop and android phones) in open public networks. But yes in relatives WiFi’s or my mobile data.

Is there anything about syncthing security I should be aware?

No, you’re fine regardless of network type or whether it’s public or not.