https://www.bleepingcomputer.com/news/microsoft/microsoft-to-fix-windows-7-black-wallpaper-bug-for-esu-customers/

Microsoft says that a bugfix will be provided for organizations that purchased Windows 7 Extended Security Updates (ESU) to fix a newly acknowledged issue leading to the desktop wallpaper being replaced by a blank black screen.

Windows 7 also reached its End of Life on January 14, therefore there will be no other bug fixes or free security updates from now on.