8083 shows as 'Stealth' and local accessing brings up a cleared login window without any credentials. From what I get from the following off the link you provided, I should be OK in that regard:
Vulnerability:
Due to an unknown bug, which occurs by every indication during the
installation and/or upgrade process, port 8083 will often open,
allowing for direct bypass of authentication to the "classic Linksys
GUI" administrative console for remote unauthenticated users.
I think I'll stick with the roll-back 'Classic' for now. After all these years, it still provides a familiar comfort.
Thanks again for your time and "guidance" - much appreciated!