I have change the Batch size for Magento 2.4
var/www/html/Mag/app/code/Reg/Indexer/etc/adminhtml/di.xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<type name="Magento\Catalog\Model\Indexer\Category\Product\Action\Full">
<arguments>
<argument name="batchRowsCount" xsi:type="array">
<item name="configurable" xsi:type="number">500</item>
<item name="default" xsi:type="number">500</item>
</argument>
</arguments>
</type>
</config>
On running the indexer process it gives an error
Category Products index PHP Fatal error: Uncaught Error: Unsupported operand types in /var/www/html/Mag/vendor/magento/framework/Indexer/BatchSizeManagement.php:49 Stack trace: #0 /var/www/html/Mag/vendor/magento/module-catalog/Model/Indexer/Category/Product/Action/Full.php(269): Magento\Framework\Indexer\BatchSizeManagement->ensureBatchSize(Object(Magento\Framework\DB\Adapter\Pdo\Mysql\Interceptor), Array) #1 /var/www/html/Mag/vendor/magento/module-catalog/Model/Indexer/Category/Product/Action/Full.php(227): Magento\Catalog\Model\Indexer\Category\Product\Action\Full->reindexCategoriesBySelect(Object(Magento\Framework\DB\Select), 'cp.entity_id IN...', Object(Magento\Store\Model\Store\Interceptor)) #2 /var/www/html/Mag/vendor/magento/module-catalog/Model/Indexer/Category/Product/Action/Full.php(192): Magento\Catalog\Model\Indexer\Category\Product\Action\Full->reindexRootCategory(Object(Magento\Store\Model\Store\Interceptor)) #3 /var/www/html/Mag/vendor/magento/module-catalog/Model/Indexer/Category/Product/Actio in /var/www/html/Mag/vendor/magento/framework/Indexer/BatchSizeManagement.php on line 49
Any help is appreciated.