You can use the get_users
function with date_query
!
$month_users = get_users(array(
'date_query' => array(
array(
'after' => 'first day of this month',
'before' => 'last day of this month',
'inclusive' => true
),
),
));
if(!empty($month_users))
{
foreach($month_users as $k => $v)
{
echo 'User : '.$v->display_name.'<br>';
}
}