Pay attention with Windows 10 SDK Installer when Upgrading 10 Seattle
After upgrading RAD Studio 10 Seattle or C++ Builder 10 Seattle to Update 1, the Windows 10 SDK installer may be launched with just one option: Remove the Windows SDK product entirely.

Please do not remove the Microsoft Windows 10 SDK from your system, as it could remove a couple of necessary files for some C++ projects.
We will provide further information soon.
Thanks
This warning should have been part of the installation!