ms office files backed up?

You can sync Word and Excel files with iCloud Drive the same way as you can sync any other files. With iCloud Drive turned on, save the files to the iCloud Drive folder (or subfolders) on the Mac; if you have the Desktop and Documents option turned on, files saved to the Desktop or to the Documents folders (or subfolders) are also synced with iCloud.

See information in Set up iCloud Drive - Apple Support

and Store files in iCloud Drive on Mac - Apple Support

Regarding terminology of "backup"

There is no iCloud "backup" for Macs. 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 the Apple article: How to back up your Mac - Official Apple Support

And more information on syncing in:

Set up and use iCloud Photos - Apple Support

and

Set up iCloud Drive on all your devices - Apple Support

and

Add your Desktop and Documents files to iCloud Drive - Apple Support