getTableHeader example

'#fields' => array_keys($field_definitions),
      '#extra' => array_keys($extra_fields),
    ];

    if (empty($field_definitions) && empty($extra_fields) && $route_info = FieldUI::getOverviewRouteInfo($this->entity->getTargetEntityTypeId(), $this->entity->getTargetBundle())) {
      $this->messenger()->addWarning($this->t('There are no fields yet added. You can add new fields on the <a href=":link">Manage fields</a> page.', [':link' => $route_info->toString()]));
      return $form;
    }

    $table = [
      '#type' => 'field_ui_table',
      '#header' => $this->getTableHeader(),
      '#regions' => $this->getRegions(),
      '#attributes' => [
        'class' => ['field-ui-overview'],
        'id' => 'field-display-overview',
      ],
      '#tabledrag' => [
        [
          'action' => 'order',
          'relationship' => 'sibling',
          'group' => 'field-weight',
        ],
        [