Page 153 in the Kindle book says: “You can run Designer from where it is located, or move it into your Applications folder so it is available to launch from the macOS Launchpad.” I just installed Qt 5.15.1 on my Mac and dragged (drug?) designer.app to the Applications folder with Finder. MacOS displayed the “Problem Report for designer” dialog every time I tried to open it. I moved it back to the /clang_64/bin folder. (Not easy. Dragging an app in Finder just creates an alias in the destination folder. Had to move it with Terminal.) It opens with no problem there. Guess it must look for other things relative to the folder where it’s installed. I created an alias and moved it to the Applications folder. That works.