I just ordered a Samsung T5 500GB SSD portable drive to add another layer to my back-ups. It has a USB C connector. If I buy a USB C to Mini-b cord, can I download directly from the camera to the drive?
I also have a D750 which was why I was able to make a quick response.
It would not surprise me it some more modern cameras may allow a direct unload via a cable to a portable drive.
Then again, I think they make SSD portables (made for photographers) that will indeed read a memory card.
If you are looking for a field backup there are portable battery operated hard drives that automatically backs up SD cards. I've tried the WD disk. It works but is expensive