Error Starting R on Mac

I have the latest version of XCode for Mojave. Nothing has changed since two days ago when everything worked. The only intervening event is the automatic security upgrade to OSX.

Let me explain precisely what happens when I try to start RStudio: A window opens with the error message. (I have uploaded an image of the window.) There is no debug information, no chance to load RStudio for debugging. Nothing. Just the error window. When I close the window, RStudio closes.

Again, I have updated R and do not have redundant installations. R runs fine either from or from Terminal.