Even though there was no indication of any GUI response elements, I tested my hypothesis that it was just a poorly-designed screen... by making sure that the last item in the GUI box (displaying the various packages to be removed -- as it said -- either obsolete or no longer needed) was selected.
Then I tabbed watching to see if the topmost element on the page was selected and it was not. I tabbed again... still no response on the screen. The third tab took me to the first item at the top of the screen.
That confirmed my hypothesis that "invisible" elements (like "OK" or "Cancel" buttons) were, indeed, on this screen. Attempting to change the window size (in the hope of revealing the missing elements at the bottom of the screen) failed. It (the window) had been designed and/or written to be of fixed size.
I was very happy to have learned of the cause... so, I guessed, the second of the 2 missing elements should be the "OK" button (although, these days I find that it appears first of the 2 (OK, Cancel) about 10% of the time.
So, when you are asked a question in a dialog box and you see no way to answer said question, try exploring to see if the missing items are, in fact, present.