8 – Unable to create a custom form tableselect

    /**
     * An example controller.
     */
    class GenerateCertificateTable extends ControllerBase {
    
      /**
       * Returns a render-able array for a test page.
       */
      public function content($nid) {
            $query = Drupal::database()->select('users_field_data', 'u');
            $query->fields('u', ('uid','name','mail'));
            //For the pagination we need to extend the pagerselectextender and
            //limit in the query
            $pager = $query->extend('DrupalCoreDatabaseQueryPagerSelectExtender')->limit(10);
            $results = $pager->execute()->fetchAll();
            // dump($results);
            // Initialize an empty array
            $header = (
                'uid' => t('UID'),
                'mail' => t('mail'),
                'name' => t('Username'),
            );
            $output = array();
            // Next, loop through the $results array
            foreach ($results as $result) {
             if ($result->uid != 0 && $result->uid != 1) {
                $options($result->uid) = (
                    'uid' => $result->uid,
                    'mail' => $result->mail,
                    'name' => $result->name,
                );
             }
           }
        
           $form('table') = (
            '#type' => 'table',
            '#header' => $header,
            '#options' => $output,
               '#js_select' => TRUE,
              '#multiple' => TRUE,
              '#required' => TRUE,
            );
            // Finally add the pager.
            $form('pager') = array(
              '#type' => 'pager'
            );
       $build() = $form;
return $build;
 }
}

I am trying to create table form using tableselect element but even after I get the data it shows empty data value.