str_shuffle() is still available in PHP 8.4 and PHP 8.5, and its behavior has not changed. It randomly shuffles the characters in a string and returns a new string. The official documentation does not list this function in the deprecation lists for PHP 8.4 or PHP 8.5.
Basic Example (Official Documentation)
<?php
$str = abcdef ;
$shuffled = str_shuffle($str);// Output is random, for example: bfdaec
echo $shuffled;
?>