Would we be able to perform MySQL Server upgrade without impacting the application?

Yes, you can upgrade Oracle MySQL version from 5.7.x to 5.8.x OR 8.x (but there is a prerequisite – PHP does not support MySQL 8.x’s caching_sha2_authentication method yet and you would have to use mysql_native_password method) and here are the steps how you can apply this change in the application (PHPKB Software).

1. Log in to Administrator Control Panel as Superuser and go to Manage Settings > General tab > Database Settings section (keep this window open as we will need it for updating MySQL details after we will upgrade MySQL Server).
2. Take the PHPKB database (and/or other databases if any) backup first and then perform the MySQL Server upgrade (as you planned).
3. Restore the database(s) that you backed up at Step 2. Note: You can also create a database user for PHPKB database.
4. Update the database details under Database Settings section (that you had opened at Step 1). Note: After saving the settings, you will be logged out from the application and that is completely normal, just do log in again.

That’s all! Now you can test and see how things work.