specific webform permissions

You can create a small custom module using this hook:

https://github.com/backdrop-contrib/webform/blob/136c20cb1c51cea203f3f0bc5355237c1d4dbf84/webform.api.php#L652-L678

/**
 * Determine if a user has access to see the results of a webform.
 *
 * Note in addition to the view access to the results granted here, the $account
 * must also have view access to the Webform node in order to see results.
 * Access via this hook is in addition (adds permission) to the standard
 * webform access.
 *
 * @param $node
 *   The Webform node to check access on.
 * @param $account
 *   The user account to check access on.
 *
 * @return bool
 *   TRUE or FALSE if the user can access the webform results.
 *
 * @see webform_results_access()
 */
function hook_webform_results_access($node, $account) {
  // Let editors view results of unpublished webforms.
  if ($node->status == 0 && in_array('editor', $account->roles)) {
    return TRUE;
  }
  else {
    return FALSE;
  }
}

Up to you how you want to limit it: perhaps a list of node IDs or using some field or property of the node or user account.

As this adds permission, you'll want to deny access to the webform results in permission, and then use this to selectively grant.