Windows Server 2012 R2 to build .NET 5 with WinRT API?

# How to set TFMs on Windows Server 2012 R2?

https://blogs.windows.com/windowsdeveloper/2020/11/10/announcing-c-winrt-version-1-0-with-the-net-5-ga-release/
In the above article said the following are supported(only?) to enable WinRT API
net5.0-windows10.0.17763.0 (Windows 10, version 1809)
net5.0-windows10.0.18362.0 (Windows 10, version 1903)
net5.0-windows10.0.19041.0 (Windows 10, version 2004)

While my build server is Windows Server 2012 R2, after I set the TFMs to net5.0-windows10.0.19041.0, it said cannot find the SDK, my thought
1, I cannot find any article said I can set a net5.0-windows2012.xx.xxx.xx.
2, I don't want to install a windows10.0.19041.0 on Windows 2012(it's not reasonable).
3, I don't want to upgrade the stable build server Windows 2012 R2 to latest such as Windows 2019?

what should I do?

p.s. I think same issue is on Windows 8.1