Looking around it’s apparent that this prefs thing is still the problem. The game is unable to create a prefs.xml file on install/first run. Do you have any cloud sync installed on the PC, such as OneDrive that syncs your Documents folders?
Uninstall Zwift, delete the entire Zwift folder within Documents, reboot the PC to check the folder is actually gone and then start over with installing Zwift. Is that what you did?