As a workaround in future you should be able to open the Unity7 desktop file manager in a Unity8 window by: nautilus -w -- --desktop_file_hint=unity8
However nautilus is crashing right now. Looks like a simple bug 1603923
As a workaround in future you should be able to open the Unity7 desktop file manager in a Unity8 window by: file_hint= unity8
nautilus -w -- --desktop_
However nautilus is crashing right now. Looks like a simple bug 1603923