Alrighty guys - here is the solution...
If anyone else is struggling with this, this will fix ya right up.
It is not enough to move the Photos Library.photoslibrary back to the original location. Once you put it there, do this.
Double click on it. That will open the Apple Photos app. Then open up the preference for that program. Click on Use as System Photo Library.
For good measure, I restarted the computer at this point. Not sure I would have had to.
Now, clear the preferences in Affinity Photo per the above. Press and hold ⌃(ctrl) while launching it, then select Clear from the dialog that will open, as Barninga suggested above.
I again restarted to be sure I was working with a clean slate.
Then I opened Affinity Photo, the media browser under the View Menu, and it worked exactly as expected.
And this ends my ability to post. So would be grateful if a moderator would raise my limit please.
Thanks to all who worked to help me.