Asking for a friend. ;)
Is there a Graphical User Interface available to upload something to a pod, like kubectl cp does?
I am either thinking of a desktop application like WinSCP, Filezilla or Cyberduck,
or a very simple webapp, i.e. deployed as a pod. I'd then mount the volume to a path and the user may upload files via the simple web interface.
I severely doubt it. kubectl cp is actually more or less just an alias for kubectl exec -t tar ... and then it pipes in a tarball datastream. It's not even on the same level as SCP, let alone more "real" file transfer protocols. It's mostly intended for debugging and not anything serious. Real file management should probably happen via persistent volumes of some kind, probably whatever hosted NFS product your cloud offers.