You can sync files with iCloud Drive. See: Set up iCloud Drive - Apple Support and Access and manage your files in iCloud Drive - Apple Support
Note that if you only want to sync some files, do not turn on the Desktop and Documents option; simply save or move those files to the iCloud Drive folder in Finder.
Also note: 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.