Migrating the documents folder to a new computer

Open Finder, is it there?

I'm that guy who does many thing the low tech way for such simple tasks so if it were me, I'd use Finder to put the files on an external disk, after copying attach the drive to the new Mac then use Finder to copy them over.

Why are you trying to do this within the Home folder? Finder is there to make things simple: Documents folder to Documents folder in the left panel.

Of course you can use the Migration Assistant, but a simple two part copy has always been the simplest most direct method for me. If you have more than just documents, MA may be a better choice.

And keep in mind that M.A. transfers only all or none. It will not allow for transfer of selected files, folders, etc.