How do I sycronize some (not all) files from my Macbook into my Icloud?

There isn’t an automatic means to sync some files, past what is described here:

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

It is possible to archive copies to iCloud Drive on a schedule, though that takes a little scripting.

There are also add-on tools which can sync files. See if Carbon Copy Cloner meets your needs here, for instance.

Time Machine backs up to local storage or to local network-attached storage, and not to iCloud.

Mac doesn’t back up to iCloud. Previous reply links to iPhone and iPad and iPod touch backups, and not Mac.

Quangle30 Said:

"How do I sycronize some (not all) files from my Macbook into my Icloud?"

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Disable or Enabled Items in iCloud:

Enable only the type that you want to upload. Elsewise, it will upload, if not disabled. Go Here: What does iCloud Back Up? - Apple Support

Select some files Select items on your Mac screen - Apple Support that are not be synced with iCloud and move to another location see the article Work with files and folders in iCloud Drive – Apple Support

Make sure iCloud Drive and desktops and documents box is turned on Use iCloud Drive to store documents on your Mac and iOS devices - Apple Support

If you enable iCloud Drive on your Mac (but without enabling the option "Desktop & Documents), you can add iCloud Drive to the sidebar in the Finder like an external volume.

Then you can drag selected Files and folders to the iCloud Drive icon. These items will be moved to iCloud Drive and mirrored on your Mac. The items on iCloud Drive will be in sync with the shadow copies on your Mac. It is not compulsory to sync the complete Documents folder and Desktop with iCloud Drive. You can just move selected items to iCloud Drive.

If your Mac should get damaged or stolen you can recover these files from iCloud Drive, but not, if you accidentally delete them.