Namely, if you install OS Catalina, you will no longer be able to uninstall, reinstall, or activate old versions of Lightroom, since the installers for these are 32-bit applications, and Catalina only supports 64-bit applications. While Adobe is working to make the latest version of Lightroom Classic compatible with Catalina, there are serious issues with using old versions of Lightroom that will not be fixed. Apple plans to introduce its new Mac operating system, OS Catalina, in late September.