Apple's iCloud upsell is far worse than Microsoft's to boot. To disable:

MS / Windows 10: Uninstall the preloaded OneDrive app in the standard way

Apple / macOS Catalina: Reboot to recovery, mount the system drive (avoiding SIP etc), use Terminal to move a plist from the System LaunchAgents - named "followupd", in case you thought it wouldn't be hidden / obfuscated. Unmount and reboot, praying you didn't break your OS. Then delete a few preference files for System Preferences.app. Oh, and likely have to repeat the process after updates

Which one would you be comfortable helping a less technical person do? And given the trajectory of macOS, I wouldn't be surprised if they close that "loophole" soon...