The new Windows Server 2019 has been already made available by Microsoft and the first problem i encountered was rather strange. When you attempt to change the product key for your Windows Server 2019 GUI version you will get the frustrating message that the key is not for the version of Windows Server you installed.
You can always change the product key using the slmgr.vbs script.
slmgr.vbs /ipk #####-#####-#####-#####-#####
slmgr.vbs /ato