how can I delete a folder on the desktop without deleting it permanently?

You can't actually delete without deleting.

You can move the folder to another folder. Like your User Profile folder, your documents folder etc.... It does not need to live on the desktop if you don't want it to.

Just open Finder, and drag the folder into whatever other folder out external drive you want to put it in.

Deleting a folder from macOS means it and its contents are gone after you empty the Trash. Either copy (drag) the folder and its contents to an external device, copy the folder contents (again drag them) to an external device, or ensure it is backed up on Time Machine, all before you delete the folder.