Use below code:

    public function execute(\Magento\Framework\Event\Observer $observer)
    {
          $order = $observer->getEvent()->getOrder();
          $order_id = $order->getIncrementId();
         foreach($order->getAllItems() as $item){
                 $ProdustIds = $item->getProductId();
         // product name
         $proName[] = $item->getName(); 
    
    
        $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $customProduct = $objectManager->get('Magento\Catalog\Model\Product')->load($ProdustIds);
    
         $productAttributeId = $customProduct->getData('attribute_set_id');
    
        //get attribute set name for each product
         $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
        $attributeSet = $objectManager->create('Magento\Eav\Api\AttributeSetRepositoryInterface');
        $attributeSetRepository = $attributeSet->get($productAttributeId);
        $attribute_set_name = $attributeSetRepository->getAttributeSetName();
        $attribute_name = strtolower($attribute_set_name);
    	
    	$StockState = $objectManager->get('\Magento\CatalogInventory\Api\StockStateInterface');
        echo $StockState->getStockQty($customProduct->getId(), $customProduct->getStore()->getWebsiteId());
    
        //get prodcut price
        $productAttributePrice = $customProduct->getData('price');
        //product qty
        $productAttributeQty = $customProduct->getData('qty');
        $proQty[] = $item->getQty();