Microsoft has released the KB4539602 update to fix a bug that caused Windows 7 wallpapers in ‘Stretch’ mode to display a blank black screen. Windows 7 users must have the SHA-2 update (KB4474419) installed and then restart your device before you apply this update. Microsoft released the last free Monthly Rollup, KB4534310, on January 14th, 2020, which includes the final quality updates and free security updates for Windows 7 before the operating system reaches the end of life.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-releases-windows-7-update-to-fix-wallpaper-bug/