Welcome to the forum.
I use Norton 360 and like you received the cryptic notification that Norton is no longer supported with the new OS and that Defender was enabled. That in fact is not the case; although you can now run both Defender and Norton together if you wish.
To get mine going again, I opened Norton with the Desktop icon (although you could also do this by clicking Start then selecting Norton from the list of installed apps), then I ran a live update. This downloaded some updates. After that I right-clicked on Norton's icon in my System tray and selected enable for both the firewall and auto-protect modes.
I've not used Norton Security version however, I imagine the process would be similar if not the same.
It is definitely working because as soon as I did that the first thing Norton wanted to do was add itself to the Internet Explorer toolbar. I don't generally use Internet Explorer, but to test things I allow Norton to add the toolbar and the Safe Search features ( 2 of the 4 options it can add ) and both work fine in IE.