How to turn off iCloud backup without losing desktop files

As per the article https://support.apple.com/en-in/HT204215

Don't edit, relocate, rename, or extract content from your backup files, because these actions might ruin the files. Use the following sections to make copies of your backups or delete backups that you no longer need.

Copy backups to another location

If you need copies of your backups, you can find the Backup folder and copy the entire folder (not just part of it) to another place, like an external drive or network-storage location.

When you use Time Machine, it automatically copies your Backup folder when you back up the Home folder on your Mac.

To avoid ruining any of your backup files, here's what you should know:

• The Finder and iTunes save backups to a Backup folder. The location of the Backup folder varies by operating system. Though you can copy the Backup folder, you should never move it to a different folder, external drive, or network drive.
• Don't edit, relocate, rename, or extract content from your backup files, because these actions might ruin the files. For example, to restore from a relocated backup file, you need to move it back or the file won't work. Backups serve as a safe copy of your entire device. So while you might be able to view or access a backup file's contents, the contents usually aren't stored in a format that you can read.

It will be easier, if you move all files and folders from the Desktop to new folder "My Desktop" in your Home folder. Just create this folder in a location, that does not sync with iCloud Drive, not on iCloud Drive, not on the Desktop, not in your Documents folder.

Save all files and folders from iCloud in local folders on your Mac by dragging them from iCloud to the local folders. This will have the advantage, the files will be gone from iCloud immediately. Then turn off iCloud Drive in your System preferences.