HOW TO BACK UP TIME MACHINE USING ICLOUD

Time Machine will not backup to iCloud. Also see the following from Back up your Mac with Time Machine - Apple Support

Connect one of the following external storage devices, sold separately. Learn more about backup disks that you can use with Time Machine.

• External drive connected to your Mac, such as a USB or Thunderbolt drive
• Network-attached storage (NAS) device that supports Time Machine over SMB
• Mac shared as a Time Machine backup destination
• AirPort Time Capsule, or external drive connected to an AirPort Time capsule or AirPort Extreme Base Station (802.11ac)

Additionally, be aware that Apple offers iCloud Backup for iPhones and iPads but not for Mac computers.

It is possible to sync data from a Mac to iCloud if you turn on those options (e.g., iCloud Photos, iCloud Drive including the Desktop & Documents option). Syncing has some of the benefits of a backup (and the benefit of being offsite) but is not the same as a backup. Major differences include the fact that not everything on your Mac can be synced and the fact that if you delete something, accidentally or otherwise, there is only a limited time period (30 days in most cases) during which it can be recovered.

Also see: https://support.apple.com/mac-backup

And more information on syncing in:

Set up and use iCloud Photos - Apple Support

and

iCloud Drive FAQ - Apple Support