Today, Microsoft released KB5001478 to Windows Insiders on the Dev channel. That's it; that's the story. It's a cumulative update for Windows 10 Insider Preview build 21332, which was released last week, and there is absolutely nothing that's new in it.
Even the idea of a cumulative update with nothing new is nothing new. Microsoft pushes out these updates pretty frequently, simply saying that they exist to test the servicing pipeline. And while that's a totally legitimate and necessary thing to do, there have been a number of cases where there were some behind the scenes changes being made.
While there's nothing new in today's cumulative update, there wasn't even much in the full build last week. Along with a bunch of fixes and minor improvements, it did put the nail in the coffin of Paint 3D and 3D Viewer. Those upgrading to the build won't lose them, but clean installations won't get them. The two apps will continue to be available through the Microsoft Store, and the news actually comes on the heels of the 3D Objects folder being removed in Windows 10.