Mohave macOS App Store will not update or download apps

After the upgrade to macOS Mohave the macOS App Store no longer will update, or download, any apps. When I try to do either an update, or a download of a new app, the icon for the app changes to the circle with the square blue stop action icon in the middle of the circle, but nothing ever happens, there is no update progress indication. If I hit the blue square to "stop" the download the icon changes back to the cloud icon.

This is on my work iMac, App Store worked perfectly before the Mohave upgrade (in fact I downloaded the Mohave upgrade via App Store on this exact machine). After the upgrade App Store is dead in the water for updating any apps, or downloading new apps to my work machine. And no, nothing changed on the work network. Literally App Store went from working to download the Mohave upgrade to broken as soon as I logged into the iMac after the Mohave upgrade.