https://wccftech.com/likely-no-new-windows-10-build-for-insiders-in-the-next-few-week/

Microsoft's Windows development team has released Windows 10 Cumulative Update Build 21390.1000 (KB5004071) for Insiders in the Dev Channel. The company clarified that the update does not include anything new and doesn't include any fixes. It is designed exclusively to test the servicing pipeline, which the company has started doing quite often.

The team intends to do that even more now, trying to test multiple cumulative updates for Build 21390. "We have been testing our servicing pipeline with Cumulative Updates to the builds released to the Dev Channel," the Windows development team wrote. "Each week, we would release a new build and then follow up with a Cumulative Update on top of that build before moving to the next build."