Win10 Search from Start shows a black box

This was an issue with the online Search service.

We are aware of a temporary server-side issue causing Windows search to show a blank box. This issue has been resolved for most users and in some cases you may need to reboot your machine.
https://internal.support.services.microsoft.com/en-us/help/4540664

This issue was resolved at Feb 05/2020 12:00 PM PST. If you are still experiencing issues, please restart your device. In rare cases, you may need to manually end the SearchUI.exe or SearchApp.exe process via Task Manager. (To locate these processes, select CTRL + Shift + Esc then select the Details tab.)
https://docs.microsoft.com/en-us/windows/release-information/windows-message-center#387