How to turn off iCloud Drive, but save existing content locally?

Unless you elect to optimize storage, all of your iCloud content remains on your device.

If you disable. Desktop & Documents, new folders are created and the previous content moved into iCloud Drive folder only. You can copy/paste from there. Or, you can create temporary folders for Desktop and Documents in your user. account and temporarily move items there before disabling).

Antifon wrote: … upon turning off iCloud Drive, temporary archive folders are created - which didn't happen.

There's a difference between turning off syncing of Desktop & Documents, and turning off iCloud Drive.

As muguy said, if you turn off syncing Desktop & Documents, then the folders remain in your iCloud Drive with all the contents, and new empty D&D folders are created in your user folder, back to normal. If you want, you can copy the stuff from the non-synced folders in iCloud Drive to the new folders.

If you turn off iCloud syncing altogether, then all your stuff is saved at iCloud.com, and you could download your stuff from there to your computer. Downloading over the internet seems awkward to me, so personally, I would copy everything to my computer before turning off iCloud. Like between any folders on a Mac, if you drag stuff from the iCloud Drive folder to your user folder, then it will be moved rather than making an extra copy.

See this:

Understanding iCloud Drive - Apple Community