I am using Mac OS Catalina, And I know its an Issue with this OS Because it didnt happen in OS Mojave.
Everytime i try to update X-Plane 11, I get messages that say the installer is not able to write to required paths and correct the file permissions in the file browser (Finder). Once i get through those messages, the installer then says it can Proceed with the update because Of the error (Error: Permission Denied. Perhaps you do not have access to a directory or file system