get all values from a multidimensional array, either by key or all.

array_value_recursive.php

<?php

if (!function_exists('array_value_recursive')) {
    /**
     * Retrieves values from a multidimensional array, either by key or all values.
     */
    function array_value_recursive(array $arr, ?string $key = null, bool $unique = true): array
    {
        array_walk_recursive($arr, function ($v, $k) use ($key, &$val) {
            if (is_null($key) || ($key && $k == $key)) {
                $val[] = $v;
            }
        });

        return $unique ? array_unique($val ?? []) : $val ?? [];
    }
}