https://arstechnica.com/gadgets/2021/09/misbehaving-microsoft-teams-ad-brings-down-the-entire-windows-11-desktop/

Microsoft released a new build of Windows 11 to Windows Insiders late last week as it prepares for the operating system's release on October 5, but the first testers to install the new build quickly ran into problems—the taskbar, desktop, Settings app, and other core OS components were refusing to load. Microsoft quickly published a registry edit that resolved the problem, but the company didn't go into more detail on what went wrong.

The most thorough examination of the problem comes from developer Daniel Aleksandersen's Ctrl blog. As he explains, the "IrisService" mentioned in Microsoft's registry edit is part of the Windows Spotlight service, which is responsible for fetching new lock screen wallpapers and other suggestions and advertisements. In Aleksandersen's own words: