Updating your Elastic Beanstalk environment’s platform …

Find and fix any application compatibility issues that you couldn’t discover during the development phase. Ensure that any customizations that your application makes using configuration files work correctly in the new environment. These might include option settings, additional installed packages, custom security policies, and script or …

https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/using-features.platform.upgrade.html