If the item is on the desktop, Control-click it, then choose Share from the shortcut menu.
In the Share menu, choose how to share the item.
The options listed depend on the type of item you’re sharing. For example, when an image in the Photos app is selected, you can choose Set Wallpaper to set the image as your desktop picture.
If you’re sharing a document created in an app that supports collaboration, you can choose Collaborate to send an invitation to work together on the document or Send Copy to just send the document.
To customise the Share menu, choose Edit Extensions.
If asked, provide additional information for the sharing method you chose.
On your Mac, choose Apple menu Use iCloud to share and collaborate on files and folders