Searching in dashboard, each view (being inside the dashboard) uses the typed text for searching in table/slice the view tied to. If there is no rows matched, it just shows nothing.
Desktop View is currently a preview feature and under active development. Preview features are not yet suitable for use in important apps. Until it has achieved greater stability, I recommend against using this preview feature except for testing and to help the AppSheet developers in their efforts. To follow the progress of and contribute to the development effort, please visit this dedicated Community topic: