The only comment I have for you is DON'T uninstall Lightroom 6 thinking that you can reinstall it because it won't work. The installer is 32--bit, and Catalina won't run the installer. You'll have to find some other solution to get Lightroom to function.
Outside of Lightroom, on your MAC bring up System Preferences, select Security and Privacy, select Privacy tab, scroll down to Files and Folders, for Lightroom make sure all media are checked. The one for removable media is probably the issue.