The system requirements for Dorico 4 can be found here:
The minimum version of macOS that Dorico 4 will run on is currently 10.14 Mojave.
The next major version of Dorico, to be released later this year, will require 10.15 Catalina. This is due to a change in the requirements of the latest version of the Qt application framework on which Dorico relies.
Here is a support document from Apple that lists the models of Mac that are compatible with Catalina:
We’re sorry for any inconvenience this may cause, and want to provide as much notice as possible of this forthcoming change in Dorico’s system requirements on macOS.