Microsoft has released a new Windows 10 Preview Build of the SDK to be used in conjunction with Windows 10 Insider Preview (Build 18985 or greater)

The Preview SDK Build 18985 contains bug fixes and under development changes to the API surface area.

Things to note:
This build works in conjunction with previously released SDKs and Visual Studio 2017 and 2019. You can install this SDK and still also continue to submit your apps that target Windows 10 build 1903 or earlier to the Microsoft Store.
The Windows SDK will now formally only be supported by Visual Studio 2017 and greater. You can download the Visual Studio 2019 here.
This build of the Windows SDK will install on only on Windows 10 Insider Preview builds.
In order to assist with script access to the SDK, the ISO will also be able to be accessed through the following static URL: https://software-download.microsoft.com/download/sg/Windows_InsiderPreview_SDK_en-us_18985_1.iso.

  Windows 10 SDK Preview Build 18985 released