Gianni-you were correct in that the WUHIDESHOW.DIAGCAB Hide Show tool requires the Windows Update Service to be running (an internet connection) in order to show the updates on the list.
But unfortunately, even though I successfully "hid" the 2018 Cumulative Update KB4056892", and it showed up in the hide/show tool as being hidden, Windows Update just charged ahead anyhow and began downloading, got to 100% download, and then began installing this update on my system until I quickly disabled windows update service again. Maybe your results are different. Or maybe (just guessing, I don't know) it's because this update is considered an "emergency" update and Win10 forces it to download and install.
So for now, I think my only recourse is to keep windows update service disabled and hope for a fix from MS.