MS loves fixes, but in order to fix something, they have to break it first and keep it broken for a while.
I think they did it because they still haven't figured out how to fix Windows' screwed up icon cache problem, so, they figured, the hell with it, lets just ditch the cracked open folder look!!!
UPDATE 4/14: Windows 10 Insider Preview Dev Build 21359.1 (co_release) - April 14
Source: https://blogs.windows.com/windows-insider/2021/04/07/announcing-windows-10-insider-preview-build-21354/
Microsoft has released an ISO file for...
UPDATE 4/15: Windows 10 Insider Preview Fast Build 19608.1000 - April 15
Please post questions and issues that are unrelated to this specific Windows 10 Insider build in the Windows Insider forum area instead.
UPDATE 4/14: KB4550936 for Windows 10 Insider Preview Slow Build 19041.207 April 14
Source: Releasing Windows 10 Insider Preview Build 19041.173 to the Slow ring | Windows Experience Blog
Direct download links for KB4552455 CAB file...