As expected, Apple has started shipping new Macs with macOS 10.15 Catalina. We’re still hesitant to recommend upgrading to Catalina, particularly if you use Mail, since reports of email data loss continue. Luckily, downgrading a new Mac from Catalina to 10.14 Mojave is possible for models other than the 16-inch MacBook Pro and the 2019 Mac Pro. Mac scripting expert (and author of the new book Moving to zsh) Armin Briegel has published a guide explaining how to roll back a new Mac that ships with Catalina to Mojave. Unfortunately, the process to install Mojave isn’t straightforward, requiring a Mojave Installer USB drive. It’s particularly fussy if your Mac is equipped with a T2 security chip since you have to set up an account before you can use Security Utility to enable booting from external drives. Regardless, you will have to erase the internal drive entirely before you can install Mojave due to Catalina’s bifurcated drive structure.