Catalina needs at least to install.
(using an iPad as a second display), plus improved security. Major Warning : Catalina is the first macOS to drop all support for 32-bit applications how to update macos high sierra 10.13.6 to 10.15
Find 64-bit replacements before upgrading, or accept that you’ll lose access to those apps. If you rely on any legacy 32-bit apps, do not upgrade to Catalina – stay on High Sierra or Mojave. Catalina needs at least to install
If you have a firmware password set: