On a 2009 iMac, a 2010 MacBook air and a 2010 MacMini, all running MacOS Catalina, the Parallels Installer fails to launch after the installer package completes the download. Possible causes: Catalina is not officially supported on those Macs and was installed with DosDude1's Catalina patcher. However, this OS is fully compatible with every other app I have tried including Xcode and Bootcamp. These older Macs simply have not been tested with the current version of Parallels. They are listed as compatible on the Parallels supported system configurations. No urgency here and if you want to remove these old systems from the compatibility list that would be fine. I am just having some fun restoring a few old Macs to usability and finding out what they can do.