Undocumented in source.
gtk.FileChooserNative is an abstraction of a dialog box suitable for use with “File/Open” or “File/Save as” commands. By default, this just uses a gtk.FileChooserDialog to implement the actual dialog. However, on certain platforms, such as Windows and macOS, the native platform file chooser is used instead. When the application is running in a sandboxed environment without direct filesystem access (such as Flatpak), gtk.FileChooserNative may call the proper APIs (portals) to let the user choose a file and make it available to the application.