code: public function render_admin_options_page() {
          $default = $this->options;
          $current = $this->get_options();
          $params = array(
              'icon' => $this->get_icon(),
              'title' => $this->get_title(__('Settings', $this->get_textdomain())),
              'form_url' => get_bloginfo('url') . '/wp-admin/admin.php?page=' . $this->get_id('-settings')
          );
  
          // Update options if necessarry
          if (filter_input(INPUT_POST, 'submit')) {
              $res = $this->save_options($default);
  
              $params['message'] = true;
              $params['message_id'] = 'message_'.rand(0, 99);
  
              if ($res === true) {
                  $params['message_type'] = 'updated';
                  $params['message_text'] = __(
                      'Options were successfully updated!',
                      $this->get_textdomain()
                  );
                  $current = $this->get_options();
              }
              else {
                  $params['message_type'] = 'error';
                  $params['message_text'] = __(
                      'Options were <b>NOT</b> successfully updated!',
                      $this->get_textdomain()
                  );
              }
          }
  
          // Prepare options for rendering
          $params['options'] = $this->prepare_options_for_render($default, $current);
  
          // Render template
          echo $this->twig->render('options_page.html.twig', $params);
      }
docs: Renders default options page (in WP administration).
  
  @since 0.1.3
  @return void
  
  @todo Add `Reset To Defaults` button!