Windows 10 Disk Cleanup program allows users to quickly free up hard drive space by removing unneeded files found in a variety of system locations. Microsoft quietly added the Downloads folder as an additional option to the program. Windows 10 Insider build 19018 (20H1) release notes stated that the Downloads option has been removed from the program. It is not known if Microsoft plans on waiting until Windows 10 20H1 is released or if they will add it to Windows 10 1903 in the next cumulative update or in Windows 10 1909.499.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-to-remove-downloads-folder-from-disk-cleanup/