I performed a clean install of Win 8.1 including all the updates available from Windows Update. One of the updates, KB 2863312, is supposed to correct compatibility issues with Norton Security products. Subsequently, I installed NIS 20.4. At the end of the install process, Windows complained about compatibility with a pop-up box. Almost immediately, a Norton pop-up (not Live Update) box appeared and started downloading files. At the end of the downloading process, the Norton box switched to a message that stated the install was successful and the Win box disappeared. I did nothing during this phase except to watch.
After the slightly unusual install, everything appears and operates normally -- same as 20.4 with Win 8. The only thing unusual (and very minor) is today IE11 created a message across the bottom of the screen stating the "Vulnerability Protection" add-on is incompatible and was disabled. I checked the add-on section of IE and it shows this add-on to be enabled despite the message. Interestingly, IE did not protest when I set the add-in to enabled yesterday nor when I used the system for hours before the message.