The situation is even worse

My test Code:
$app = Factory::getApplication();
print_r($app->input->get->getArray());

URL in browser:
../administrator/index.php?option=com_test&a=int

Result:
Array ( [option] => com_test [a] => 0 )

URL in browser:
../administrator/index.php?option=com_test&a=bool

Result:
Array ( [option] => com_test [a] => 1 )

URL in browser:
../administrator/index.php?option=com_test&a=attributes

An error has occurred.

0 Joomla\Filter\InputFilter::cleanAttributes(): Argument #1 ($attrSet) must be of type array, string given, called in C:\OSPanel\home\j6\libraries\vendor\joomla\filter\src\InputFilter.php on line 248

Joomla 5 code
protected function getArrayRecursive(array $vars = [], $datasource = null, $defaultFilter = 'unknown', $recursion = false)
{
if (empty($vars) && \is_null($datasource)) {
$vars = $this->data;
} else {
if (!$recursion) {
$defaultFilter = null;
}
}

    $results = [];

    foreach ($vars as $k => $v) {
        if (\is_array($v)) {
            if (\is_null($datasource)) {
                $results[$k] = $this->getArrayRecursive($v, $this->get($k, null, 'array'), $defaultFilter, true);
            } else {
                $results[$k] = $this->getArrayRecursive($v, $datasource[$k], $defaultFilter, true);
            }
        } else {
            $filter = $defaultFilter ?? $v;

            if (\is_null($datasource)) {
                $results[$k] = $this->get($k, null, $filter);
            } elseif (isset($datasource[$k])) {
                $results[$k] = $this->filter->clean($datasource[$k], $filter);
            } else {
                $results[$k] = $this->filter->clean(null, $filter);
            }
        }
    }

    return $results;
}

Joomla 6 code

public function getArray(array $vars = [], $datasource = null)
{
if (empty($vars) && $datasource === null) {
$vars = $this->data;
}

    $results = [];

    foreach ($vars as $k => $v) {
        if (\is_array($v)) {
            if ($datasource === null) {
                $results[$k] = $this->getArray($v, $this->get($k, null, 'array'));
            } else {
                $results[$k] = $this->getArray($v, $datasource[$k]);
            }
        } else {
            if ($datasource === null) {
                $results[$k] = $this->get($k, null, $v);
            } elseif (isset($datasource[$k])) {
                $results[$k] = $this->filter->clean($datasource[$k], $v);
            } else {
                $results[$k] = $this->filter->clean(null, $v);
            }
        }
    }

    return $results;
}

Bug in code

$results[$k] = $this->get($k, null, $filter);

changed to:

$results[$k] = $this->get($k, null, $v);

Joomla 6 switched to using the framework Joomla\Input\Input implementation in place of the CMS input handling used in earlier versions.

This change exposed an issue in Input::getArray() when called without an explicit filter map. In this case, request values can be misinterpreted as filter names, leading to unexpected filtering behaviour and, in some cases, fatal errors (e.g. when values such as attributes are present).

The easiest fix might be to bring Joomla\CMS\Input\Input::getArray() and Joomla\CMS\Input\Input::getArrayRecursive() over to the framework.