Move Folder from Mac to External Drive

Copy from one drive to another is the normal order of operation.

Once a file has been copied to the other drive, you are free to delete it from the source.

Once a file has been copied to a drive it can be freely moved within or copied to other folders in that drive.

You can "move" a folder to the EHD but if there's any interruption of any sort for any reason you can lose the folder and all files in it. That's why it's best to copy/drag a folder to the EHD, verify the copy was successful before deleting it from the source drive. Like the old carpenter adage: measure twice - cut once.