So I guess I assumed Wolfram was depreciating the desktop and trying to go mobile first, as so many other companies have done. What I found after taking a deep breath is that I can create a new file in 12.1.1 and enter a "=" assignment as usual and "[Ctl]=" Euler evaluates the normal entry for Leonard E.
However, that is not what happens to any of my saved (100's) of nb files. Entering "=" converts the input cell into some alpha thingy that cannot be changed or evaluated. Entering "[Ctl]=" Euler returns a not-parsed error in some files and the normal output in other files.
I can create new input in the new nb file created under 12.1.1 then paste the expression(s) into an older file (say from Monday) and evaluate it. I can also write code in a text editor and paste it into a nb, then evaluate it correctly, so Mathematical is not brain dead, just unable to accept a typed assignment.
A work-around, such as "(2+w)/.w->3" generates another good result I've not seen before:
![result of entering](https://community.wolfram.com//c/portal/getImageAttachment?filename=ScreenShot2020-06-18at09.44.42.png&userId=1399962)
This was Mathematica install thirty-something for me, so I did it the same way I that has worked for decades. Thinking of uninstalling Mathematica with CleanMyMac and downloading 12.1.1 again. If that doesn't work, I'll try to find a file fixer utility or something...