Offloading data to iCloud Drive

You do know that the iCloud Drive is a syncing feature and not an off computer storage facility. Any file you put in the iCloud Drive is mirrored in your Home/Library/Mobil Documents folder.

So if you want to get files off your MBP to free up space use an external SSD like OWC's ENVOY PRO ELEKTRON or its ENVOY PRO FX.

As others have noted, iCloud is not an archiving service; but a synchronization across devices. If you want to archive data, use something like BackBlaze (I use it for archiving and online backup). That said, if you really want quicker access, you might want to instead offload the folder to an external drive.

A single folder with massive files / sub folders inside having size of 315 GB is avoided , try to create folder in smaller size .

The folder will get merged in iCloud Drive , when iCloud Drive and desktops and documents box is turned as on .

See the articles Use iCloud Drive to store documents on your Mac and iOS devices - Apple Support

Upload and download files from iCloud Drive on iCloud.com - Apple Support

Access and manage files in your iCloud Drive - Apple Support

To clear iCloud storage see the articles .

Manage your iCloud storage - Apple Support

Save space on your MacBook Air - Apple Support

How to free up storage space on your Mac - Apple Support

Find and delete files on your Mac - Apple Support

Apollo471 wrote:

but why can't I also offload a file into iCloud Drive to free up space on my Mac?

Because as a syncing feature it's not designed to do that.