[ubuntu] Software Updater Lockup

Somewhere (perhaps in another workspace?) there should have been a pop-up window for grub-pc stating that a newer configuration file can be installed.
It would have asked you if you wanted to install the new version of that configuration file, or keep the one currently being used.

What you might do to see if there is indeed a pop-up window hiding somewhere is to use the window switcher mechanism alt+tab > up/down key.
(To view all workspaces, use ctrl + alt + tab > up/down key.)
You use the up/down keys to view apps that may have multiple windows, since alt+tab will only show a single in the default viewer.
(If that makes any sense)