maybe my Mac is too old but the option 'Desktop and Document Folders' does not appear...
The option to add your Desktop and Documents files to iCloud Drive was introduced in macOS 10.12 Sierra.
To check your current macOS version, click Apple menu > About This Mac.
If your Mac is too old to upgrade to macOS Big Sur, the latest version, you might still be able to upgrade to macOS Sierra or another recent version.
The following Mac models are compatible with macOS Sierra: