As you are referring to “explorer” you probably are using Windows.
In that case, your friend should have a look at the Native UI wrappers for Syncthing, like Synctrayzor.
There you will be able to open the folder in explorer.
As Syncthing is cross plattform, Syncthing would need to be able to open the default file manager in every OS and desktop environment. Therefore it will probably be always something which is left to the native wrappers.