If you are using the SSO integration, you must specify a User Name Qualifier and that is why you cannot leave it empty in the configuration.
These SSO settings are used by the
SsoAgentModule. If you want to disable the SSO integration, you will have to remove that HTTP module from the CM website (and ensure an alternative authorization method is configured).
If you’re getting problems only for certain web applications/services, you should check if the
SsoAgentModule is also removed from the individual web apps within the CM website (