iCloud Drive

iCloud is a syncing system, not an external storage system. Documents in iCloud Drive are also on your computer.

If you don't want them on your hard drive, you need a different cloud based solution such as Dropbox, OneDrive, or Flicker.

See this article https://www.imyfone.com/iphone-issues/icloud-drive-takes-up-too-much-space-on-computer/

https://support.apple.com/en-in/HT206996