Upgrading EC2 Ubuntu 18.04.6 LTS Instance

In general, updates to the OS will not change application settings. That said, as you point to the repos for the new version of the OS, if the application was installed from the OS repo there may (will likely) be new versions of the application that will also get applied. New versions of the application may have configuration or feature changes.

I would advise that you take a snapshot of the instance before proceeding with the upgrade to ensure that you can recover the instance if something goes awry.