Catalina to Monterrey upgrade

You would perform a Time Machine backup of Catalina before any upgrade. Once Monterey is released, you would follow the upgrade, and first boot afterward, by providing the Catalina Time Machine backup to migrate your existing settings into Monterey.

The likelihood of early-adopting Monterey could be the absence of compatible printer/scanner applications from their respective vendors, so look before you leap. Some mainstream applications may need updates after Monterey's release for stability.

Otherwise, we cannot discuss Monterey (a beta product) at this time.

The Time Machine backup is to protect your data and settings as they were in Catalina. It is also your ticket to go back to Catalina if you want to undo the upgrade.

Although an upgrade scenario should not touch your documents, it may convert your email to the version Monterey is using, and additional changes that occur that you won't know about until you sign in after the upgrade. I never perform an upgrade without a final Time Machine backup of the prior operating system.