The latest version of Windows is Windows 11, which was released on October 5, 2021. Microsoft has been providing updates, patches, and preview builds for Windows 11 through the Windows Insider program, but there has been no official word on a successor.
As of now, there is no official Windows 12 beta version available. Microsoft has not announced any details about a forthcoming Windows 12 operating system, let alone a beta version. windows 12 beta version
That being said, I can certainly create a fictional story about a hypothetical Windows 12 beta version. Here's a detailed tale: The latest version of Windows is Windows 11,