Plugin Options Page and Subpage

If you want to use multiple options pages for plugin, ensure that your sanitize function gets the additional missing options from the database

example

public function sanitize($input): array
{
  /** My Plugin Setting Options */
  $option = get_option('my_plugin_settings');
  /** Do this for all the settings keys in your options array */
  if ($input['setting_key']) {
    $output['setting_key'] = $input['setting_key'];
  } else {
    $output['setting_key'] = $option['setting_key'];
  }

  return $output;
}

tech