Most common SAP applications are now Generally Available on Windows 2019.
Windows Operating System support is generally dependent on the SAP Kernel for ABAP system or JVM for Java Systems; SAP Support Packs usually do not need to be applied. Most SAP applications that support ABAP Kernel 7.22 or 7.53 (or higher) or JVM 6 (or higher).
The SAP Product Availability Matrix contains the required release and support information. As of March 2019 not all DBMS are certified on Windows 2019. SQL Server 2012 (or higher), Hana 2.0 client libraries and LiveCache are supported. DB2 LUW, Sybase and Oracle databases will be certified in due course
Windows 2019 includes many features deeply integrated into the Azure public cloud platform. SAP on Windows 2019 is simultaneously released for on-premises deployments and on Azure cloud deployments. The full list of Operating Systems and VM types supported on Azure is documented in SAP Note 1928533 - SAP Applications on Azure: Supported Products and Azure VM types https://launchpad.support.sap.com/#/notes/1928533
2. Azure Site Recovery Support
Azure Site Recovery fully supports Windows 2019 for the Azure-to-Azure scenario. Customers can protect SAP Applications server VMs using Azure Site Recovery
Windows Clustering includes a new feature useful for SAP customers called Azure-aware clusters. Windows 2019 cluster can receive and respond to Azure planned maintenance notifications. Windows cluster will failover services before planned maintenance events occur
Windows 2019 and Windows 2016 support in-place OS upgrades of an ASCS Cluster. The minimum source release for the cluster is Windows 2012. The following note also applies to Windows 2019 2419847 - Support of Windows in-place upgrade in Failover Cluster environments https://launchpad.support.sap.com/#/notes/2419847
5. Windows 2008 (R2) is End of Life – Plan Migration
Customers running on Windows 2008 or Windows 2008 R2 should immediately start planning to upgrade to Windows 2019. Customers running on old Java Applications (such as Enterprise Portal 7.0x) version 4 or 5 JVMs (not supported on modern OS versions) should start reviewing the different upgrade paths available.