Microsoft is blocking Windows 10 2004 upgrades due to multiple conflicts caused by older or incompatible display drivers. Microsoft will not allow the May 2020 Update to be installed until these issues are resolved. Microsoft listed two issues with Intel IGPU and older NVIDIA drivers that block the update from being installed. Microsoft says they are working with Intel to create a fix that will be released in a future update. Users can either update their display drivers to the latest available version or disable the memory integrity feature or upgrade to Windows 10, version 2004.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-2004-upgrade-may-be-blocked-due-to-old-graphics-drivers/