<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
   <preference for="MagentoCatalogBlockProductProductListToolbar" type="{vendor}{module}BlockPluginProductProductListToolbar" />
</config>

namespace {Vendor}{module}BlockPluginProductProductList;

class Toolbar extends MagentoCatalogBlockProductProductListToolbar{

$this->_collection = $collection;

$this->_collection->setCurPage($this->getCurrentPage());

$limit = (int)$this->getLimit();
if ($limit) {
    $this->_collection->setPageSize($limit);
}


if ($this->getCurrentOrder()) {


    switch ($this->getCurrentOrder()) {

        case 'created_at':

            if ( $this->getCurrentDirection() == 'desc' ) {

                $this->_collection
                    ->getSelect()
                    ->order('e.created_at DESC');


            } elseif ( $this->getCurrentDirection() == 'asc' ) {

                $this->_collection
                    ->getSelect()
                    ->order('e.created_at ASC');

            }

            break;
 case 'in_stock':
        $this->_collection
                    ->getSelect()
                    ->joinLeft(
           ['admin'=>$collection->getTable('cataloginventory_stock_item')],
           'e.entity_id = admin.product_id')->where('admin.is_in_stock = 1');


            break;
    case 'out_stock':



                $this->_collection
                    ->getSelect()
                    ->joinLeft(
           ['admin'=>$collection->getTable('cataloginventory_stock_item')],
           'e.entity_id = admin.product_id')->where('admin.is_in_stock = 0');


            break;
        default:

            $this->_collection->setOrder($this->getCurrentOrder(), $this->getCurrentDirection());
            break;

    }

}



return $this;

}