You posted on a wrong forum (Windows App SDK is for WinUI 3)
The Win32 API forum is https://learn.microsoft.com/en-us/answers/tags/224/windows-api-win32
But in 90's, it was 16-bit
You can find archives on sites like https://winworldpc.com/product/windows-sdk-ddk/windows-31
(16-bit files (with _ in extension for example) can be opened with tools like 7-Zip)