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:

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...

Good to know, but the problem occurs in Input cells, not Text cells. My solution has been uninstalling my second attempt to get 12.1.1 working and reinstall 12.1.0 The older version works like it did earlier this week, so I will stay on 12.1.0 until there is a patch.

Are you going to publish a new build of 12.1.1 once this is fixed?

A new 12.1.1 or a 12.1.2? If it's called 12.1.1, I bet many institutions will not upgrade their machines, leaving users frustrated and not understanding what happened.

Unfortunately it is also called "12.1.1". Incrementing the version number would have been much harder due to various considerations, simply replacing the builds in the user portal is quite simple for us in comparison.

Helo, David

The same thing happened to me; your blunt description was clear and accurate. I have retreated to v12.0.0

WRI should use semantic versioning for Mathematica.

Wolfram typical does not use beta testers for 'minor' updates. Perhaps they should.

I have been participating in beta tests since version 3. It is hard to catch everything, especially since the list of things to test for primarily consists of new functionality. However, this incident gives me a clue for the next beta test (12.2?, 13? or if they have Triskaidekaphobia, 14?)

I would imagine that many of the changes will be to ensure compatibility with macOS Big Sur and the release next year of Apple Silicon Macs, plus the usual bells and whistles. I would settle for fewer bugs and better integration with my hardware (I use macOS).

I share your concern about macOS support. It's no secret that Theo Gray was largely responsible for continued Mac support during the 'dark days', and the macOS seems to be getting a bit less love since he has moved on.

I did find an issue with Big Sur that indicated that the modernization of the front end is incomplete. This problem, while not trivial, is easy to fix. However, I will look with great interest about the transition to Apple Silicon. As you may recall, Wolfram (and Theo Gray) were featured in the transition to Intel, so I had no doubts that Mathematica would be ready for the transition.

My main concern is not with basic functionality, which, I am sure, a recompile with a magic switch will take care of. Mathematica currently does not make full use of Apple GPU support, which makes it harder to accelerate Neural nets and other technologies. With the switch to Apple Silicon, we will undoubtedly get custom GPUs. These will be (probably) much better, but will require the use of Apple's Frameworks to work properly. Wolfram lagged behind support of Metal for graphics, and I fear that they will also all behind in support of Apple's other frameworks. Open source is all well and good, but even the best supported open source projects can't compete with the resources Apple has.

It will be interesting. I have a newish MacBook Pro that will get me through the transition, but I do hope to get a new MacBook sometime in the next year or so.

My feeling is that with more user feedback, Wolfram may be persuaded to adjust their priorities.

Interesting times....