When Authentication Services is tested for a Windows Server version it is also tested for the latest functional level. For example, a version of Authentication Services that is tested and validated for Windows Server 2012 is also validated for Windows Server 2012 functonal level. If the Authentication Services version that is deployed supports the server level the functional level is also expected to work without additional configuration of the product.
QAS 4.1.3 - 4.1.8 has been verified on Winodws versions up to Server 2012. Please note: QAS 4.1.x is now in limited support.
For Authentication Services 4.2.x there is information on supported Windows version in the release notes of each version. Please see the following link: https://support.oneidentity.com/technical-documents/authentication-services/4.2.3/release-notes/2#TOPIC-1376246