I am running an iMac Pro with Intel silicon under the latest version of Big Sur 11.3.1. I upgraded my Mathematica from 12.2 to 12.3 yesterday, but now I have suddenly lost the ability to use the QuickLook feature with Mathematica notebooks. I click on a notebook's icon in Finder to highlight it and then touch the spacebar, just as I have done for years, but under 12.3 I get only a picture of the icon--no internal contents of the notebook is displayed. I suspect that this will also interfere with Spotlight's ability to search and index the internal contents of Mathematica notebooks on my Mac. Mathematica itself seems to run fine, and QuickLook works as normal with files that are not Mathematica notebooks.
I used my Premier Service agreement to call Wolfram Support about this problem and I spoke to a technician. He seemed to confirm that this also happens on his Mac running some version of Catalina. Neither of us could get QuickLook to display a preview of the contents of even a trivial notebook containing only the cell 2+2.
For me the ability to use QuickLook with my Mathematica notebook files is important to my overall workflow. Has anyone else experienced this problem? I tired running the command "qlmanage -r" in terminal to reset the QuickLook cache, but that didn't seem to help. Any ideas? Thanks"