Can I upgrade my operating system from El Capitan to Catalina without my Documents and Desktop files going automatically to iCloud Drive?

I have a four-year-old iMac that's running on El Capitan. I deliberately haven't upgraded the operating system because when I upgraded to High Sierra on my MacBook Pro, my Documents and Desktop files went running off to iCloud Drive as soon as the upgrade was loaded. For a number of reasons, I don't want any of my files going into the cloud – ever.

When we recently upgraded one of the installed programs on our iMac, we were informed that any further upgrades will require an upgrade in our operating system. Naturally we want to upgrade the operating system, but we don't want our Documents and Desktop going to iCloud Drive. Is there some way that we can disable iCloud Drive in advance so that we don't have those files going to the cloud and necessitating our jumping through hoops to get them back onto the computer where we want them?