Windows 10 20H1 has received Build 19613.1005 today with nothing major changes. Cumulative update KB4558320 is released to Fast ring to increase the build number.
As the release date of Windows 10 May 2020 update is closing Microsoft is running the required test. They are trying to make sure that the next big feature update may work properly in all environments. This rollout is designed to test the servicing pipeline with builds from the Active Development Branch in the Fast ring. The next update will be released in the month of May this year.
Source – Windows Experience blog.