In this collection This BEst seller give me error it’s not working, unable to sort by best seller ASC, DESC not working in this condition

public function getProductCollection()
{

    $objectManager = MagentoFrameworkAppObjectManager::getInstance();
    $filterableAttributes = $objectManager->create(MagentoCatalogModelLayerCategoryFilterableAttributeList::class);
    $attributes = $filterableAttributes->getList();

    $price=$this->getRequest()->getParam('price');
    $cat=$this->getRequest()->getParam('cat');
    $sortby=$this->getRequest()->getParam('product_list_order');
    if (empty($sortby)) {
       $sortby='position';
    }
    $listdesc=$this->getRequest()->getParam('product_list_dir');
    
    $page=($this->getRequest()->getParam('p'))? $this->getRequest()->getParam('p') : 1;
       //get values of current limit
    $pageSize=($this->getRequest()->getParam('limit'))? $this->getRequest()->getParam('limit') : 3;
    $collection = $this->_productCollectionFactory->create();
    $collection->addAttributeToSelect('*');
    $collection->setOrder('title','ASC');
    $collection->setPageSize($pageSize);
    $collection->setCurPage($page);
       
    foreach ($attributes as $attributes1 ) {
                 $attributefrontend = $attributes1->getFrontendInput();
               if (!empty($_REQUEST[$attributes1->getAttributeCode()]) && $attributefrontend=="select") {
                    $collection->addAttributeToFilter($attributes1->getAttributeCode(), $_REQUEST[$attributes1->getAttributeCode()]);
                }
               if (!empty($_REQUEST[$attributes1->getAttributeCode()]) && $attributefrontend=="multiselect") {
                 $collection->addAttributeToFilter($attributes1->getAttributeCode(), array('in' => array((int)$_REQUEST[$attributes1->getAttributeCode()])));
               }
                
                if (isset($price) || isset($cat) || isset($_REQUEST[$attributes1->getAttributeCode()]) || isset($sortby)) {

                     $pricebetween=explode("-",$price);        
                 
                   if (!empty($pricebetween[0])) {
                     $collection->addAttributeToFilter('price', array('gteq' => $pricebetween[0]));
                   }
                   if (!empty($pricebetween[1])) { 
                       $collection->addAttributeToFilter('price', array('lteq' => $pricebetween[1]));
                   }
                   if (!empty($cat)) {
                       $category = $this->_categoryFactory->create()->load($cat);
                       $collection->addCategoryFilter($category);
                       $collection->addAttributeToFilter('visibility', MagentoCatalogModelProductVisibility::VISIBILITY_BOTH);
                       $collection->addAttributeToFilter('status',MagentoCatalogModelProductAttributeSourceStatus::STATUS_ENABLED);
                   }
     
                      
                }
                if ($sortby=='position') {
                        $collection->setOrder($sortby,'ASC');
                   }
                   if (!empty($listdesc)) {
                       $collection->setOrder($sortby,'DESC');
                   } else {
                       $collection->setOrder($sortby,'ASC');
                   }
         
    }
    /*echo $collection->getSelect(); */

    return $collection;
}

In this collection This bestseller give me the error it’s not working

$collection->getSelect()->joinLeft(
            'sales_order_item',
            'e.entity_id = sales_order_item.product_id',
            array('qty_ordered'=>'SUM(sales_order_item.qty_ordered)'))
            ->group('e.entity_id')
            ->order('qty_ordered '.$subject->getCurrentDirection());