Widgets aren’t metaboxes, they can’t be added to the dashboard directly.
wp_add_dashboard_widget expects a callable function, not a sidebar ID. You can’t plug a widget or a widget area/sidebar into a function like that.
Instead, you would need to add a metabox, then, in its callback display what you wanted to display, e.g.
add_action('wp_dashboard_setup', 'custom_dashboard_widgets');
function custom_dashboard_widgets() {
global $wp_meta_boxes;
wp_add_dashboard_widget('custom_dashboard_box', 'Example', 'custom_dashboard_box');
}
function custom_dashboard_box() {
// Widget Content Here
echo '<p>Hello World</p>';
}
You could then call the_widget inside the callback to display an individual widget with predefined parameters.
Additionally, your questions code registers a sidebar, not a widget. If it’s the displaying of a widget area in the dashboard that you want, that is not what you asked. Please update your question accordingly.