MenuManager uses the each() construct which is deprecated in PHP 8.1.

Quick and dirty fix:
*** MenuManager.module.php      2023-07-25 20:24:31.380937841 +0200
--- MenuManager.module.php.orig 2023-07-25 20:21:12.312061045 +0200
***************
*** 108,115 ****
        reset($children);
        $nchildren = count($children);
        $nc = -1;
! #     while (list($key) = each($children)) {
!       foreach ($children as $key => $value) {
          $nc++;
          $onechild =& $children[$key];
          $content = $onechild->GetContent($deep);
--- 108,114 ----
        reset($children);
        $nchildren = count($children);
        $nc = -1;
!       while (list($key) = each($children)) {
          $nc++;
          $onechild =& $children[$key];
          $content = $onechild->GetContent($deep);