OK... for others that might have run into the same problem, the cause has been found.

On the MacBook, I went into the KeyChain and searched for all keychain entries related to Opera. Then deleted them.

You must reboot your system. Then go in and re-login to the sync server within the Opera app.

That fixed the issue, but after many reinstalls I really think there should be some option for a reset within the Opera App itself. Good thing is it finally worked.

Also... when signed in on the MacBook. If I go to the Preferences and click on Advanced Configuration in the Synchronization option, nothing happens and no secondary window opens.

Some time in the not to long ago past sync for bookmarks stopped working for my MacBook Pro. All iOS devices continue to sync properly, so the account is good and I can see the bookmarks on sync.opera.com/web.

I completely removed Opera (the hard way) and re-installed, but the problem remains. I tried the re-install the first time with the install wizard download and it refused to see the network, so I had to download the manual install file.

When I click on the person/account icon is says Synchronization Isn't Working, but the sync never runs.

I am not running any Firewall and have turned off Little Snitch and still no Synchronization of data into the MacBook. At this point I am lost and open to suggestions.

After all this time it is great to see an update. However, while my first impression is good, I am so deeply disappointed that bookmark syncing has not been resolved. Lack of keeping bookmarks in sync across all devices is grounds for using another browser.