If you face pagination not working issue after upgrading Magento 2.4.3 then follow below few steps.

Step 1 : Open your theme’s list.phtml file like app/design/frontend/Magemonkeys/CustomTheme/Magento_Catalog/templates/product/list.phtml

Step 2 : Find below code in the bottom section of the list.phtml file

<?= $block->getToolbarHtml() ?>

Step 3 : Replace above code with below code in the bottom section of the list.phtml file

<?= $block->getChildBlock('toolbar')->setIsBottom(true)->toHtml() ?>

Step 4 : After place above code, please run below mentioned commands

php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy
php bin/magento cache:clean

That’s it.

Now when you will refresh the category page, you will find pagination on working condition.