Updates
Intro
Installer
softwareupdate --fetch-full-installer --full-installer-version 13.0.1
Companion app
App to create configuration profile
Convert macOS property lists into configuration profiles
Downgrading Avoiding updates
You can avoid updates for your mac by adding the update server to your host file to return empty response so macOS won't be able to ping the update servers.
MDM
Or you can go for having MDM profile installed which limits your macOS to not upgrade to a specific OS or stay within the range of specific versions in the allowlist.
Apple doc around MDM restrictions
How to setup using apple configurator support article
Deploying your MDM profiles using MicroMDM quick start guide
Removing MDM Profiles
Internal Links
Read more about iOS or other non macOS MDM here
Internal documentation about software_updates
Link
apple support article around macOS updates
how-to-download-macos-catalina-mojave-or-high-sierra-full-installers/