Worked for me
I have a Windows server 2012 R2 KMS server
Added a "Windows Server 2019 Datacenter" KMS key into the KMS server
I could activate a Windows 10 enterprise LTSC machine using the generic key M7XTQ-FN8P6-TTKYV-9D4CC-J462D from https://docs.microsoft.com/is-is/windows-server/get-started/kmsclientkeys