Thanks to all who responded. Today it all fell into place. It helps that I'm a retired bum with lots of time on my hands thanks to the Corona virus.
I uninstalled EVERYTHING, Creative Cloud, Lightroom Classic, and Photoshop. I then shut the computer down (a 2013 Mac Pro "trashcan"), not a restart, a shutdown. I then restarted and reinstalled each program, starting with Creative Cloud, the Lightroom Classic, the Photoshop. When I hit the previously feared Command-E to open a TIFF from LrC, IT OPENED in PS! Then to check further, in the Finder, I right clicked on a TIFF file, and chose "open with" and instead of three versions of Photoshop (which I don't have), it just indicated Photoshop 2020. I guess the faulty launch services database got repaired. My plan to rebuild launchservices in Onyx was not needed.
A word about my workflow, if anyone cares, and an explanation of why I keep my TIFF's in LrC. I suspect many people do what I do or a minor variation.
I import my RAW ARW images into LrC; I then develop them in the develop module as best I can. As we all know there's a LOT that can be done in LrC. But I still always use Photoshop for my "Master" images, the ones that might see a frame and the wall. I take the file into Photoshop as a Smart Object (Thank you Charlie Cramer-he teaches this so one can go back to ACR and the more malleable RAW file any time and do further work that might help the image). I then do my thing in Photoshop, and save the file as a "Master" TIFF with all the PS layers back into the LrC database. The "Master" designation enables easy searches for significant images. This way, when I'm either ready to print, (I print in Photoshop using Focus Magic for output sharpening, again, Thanks Charlie) or decide it needs more work, I open the TIFF back into Photoshop.
This has been frustrating but I hope it might be helpful to someone else who finds themselves in a similar conundrum.