Solved: Class 'Zend\Serializer\Serializer' not found

Magento 2.4.3 version has been released on 10th August 2021, for both Commerce/Cloud and Open Source editions.

After upgrading to Magento 2.4.3 you may have Class "Zend\Serializer\Serializer" not found or "Zend\Serializer\Adapter\PhpSerialize" not found errors on some of your third party extensions that use "Zend\Serializer\Serializer" or "Zend\Serializer\Adapter\PhpSerialize" classes.

composer require laminas/laminas-serializer --no-update
composer update
bin/magento setup:upgrade
rm -rf var/generation var/view_preprocessed/ pub/static/frontend
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
bin/magento cache:flush