gform_editor_sidebar_panels

add_filter( 'gform_editor_sidebar_panels', 'your_function_name', 10, 2 );

add_filter( 'gform_editor_sidebar_panels_6', 'your_function_name', 10, 2 );

add_filter( 'gform_editor_sidebar_panels', function ( $panels, $form ) {
    $panels[] = array(
        // Define the unique ID for your panel.
        'id'           => 'my_custom_panel_1',
        // Define the title to be displayed on the toggle button for your panel.
        'title'        => 'My Custom Panel',
        // Define an array of classes to be added to the toggle button for your panel.
        'nav_classes'  => array( 'my_nav_class_1', 'my_nav_class_2' ),
        // Define an array of classes to be added to the body of your panel.
        'body_classes' => array( 'my_body_class_1' ),
    );
    return $panels;
}, 10, 2 );