I wanted to sign out of my apple ID from my macbook because I didn't have enough storage anymore, it warned "If you turn off the icloud drive, all documents stored in iCloud will be removed from this Mac and will be available on iCloud Drive only."

See the following from Add your Desktop and Documents files to iCloud Drive - Apple Support

What happens when you turn off iCloud Drive or sign out of iCloud

If you turn off iCloud Drive or sign out of iCloud, a new Desktop and Documents folder is created in your home folder. You also have the option to keep a local copy of your files that are in iCloud Drive. If you keep a local copy of your files in iCloud Drive, they're copied to a folder called iCloud Drive (Archive) in your home folder. You can move any files that were in your iCloud Desktop and Documents to your new local Desktop and Documents.

Note that the above is if you turn off iCloud Drive. If you leave iCloud Drive turned on but only turn off the Desktop & Documents option, see the following from the same support document:

Turn off Desktop and Documents

1. From your Mac, choose Apple menu  > System Preferences. Click Apple ID, then click iCloud. On macOS Mojave or earlier, choose Apple menu  > System Preferences, then click iCloud.
2. Next to iCloud Drive, click Options.
3. Deselect Desktop & Documents Folders.
4. Click Done.

What happens when you turn off Desktop and Documents

When you turn off Desktop & Documents Folders, your files stay in iCloud Drive and a new Desktop and Documents folder is created on your Mac in the home folder. You can move files from iCloud Drive to your Mac as you need them, or select all of your files and drag them to the place you want to keep them.