How can a Flutter desktop app properly access the native operating system's own file system, such as letting a user open or save an actual local file, using the file_picker or similar dedicated packages?

Unlike a typical mobile app which is generally quite heavily sandboxed with only fairly limited direct file system access, a genuine desktop application often needs to interact considerably more directly and freely with the actual native file system, and the file_picker package provides a consistent Flutter interface for displaying the operating system's own native file open or save dialog, letting a user genuinely browse their own actual computer's file system to select an existing file to open or to properly choose exactly where a new file should actually be saved to.

final result = await FilePicker.platform.pickFiles();
if (result != null) {
  final filePath = result.files.single.path;
  final content = await File(filePath!).readAsString();
}