Upgrading Magento from version 2.3.1 to version 2.4.5 should not have any impact on your existing pricing rules. The upgrade process should preserve your existing pricing rules, as long as the upgrade process completes successfully without any errors.
However, it's always a good practice to take a backup of your website and database before upgrading to a new version of Magento. This way, you can restore your website to the previous version in case of any issues.
After upgrading, it's recommended to test your pricing rules to ensure that they are still functioning properly. If you notice any issues with the pricing rules, you may need to update them or recreate them in the new version of Magento.
In summary, your pricing rules should work as they did before the upgrade, but it's always a good idea to take a backup and test them to ensure that they are functioning properly.