This is one issue that has vexed me since the change. I was even told months ago (back in August) the same then that Charles pointed out.
NOTE: I found out very recently, that you also need to uncheck the 'Disable helpdesk menu' option in Configuration > Helpdesk Settings > General Settings area as well to get this widget, and other helpdesk widgets, as an option.
That said, the Windows 10 Build Overview widget is lacking anyway; it should be named Windows 10 Build Details. I get the desire to all the entire build number, but it's all over the place and is a perfect example of too much information equals out to be no worthwhile information at all.
The Windows 10 Build Overview should be restricted to version numbers. IE, Windows 10 1809, Windows 10 (1803), Windows 10 (1709). Not Windows 10 (10.0.15063.1446) and Windows 10 (10.0.15.63.608) etc. (It might even be more helpful is they were in number order)
-Kris