@GossiTheDog Oops.
We had to do something similar a couple of years ago to transfer (not as much) data from someone's on-prem into Azure, and they have a service called "DataBox", where they ship some hardware with a bunch of connectivity ports on it to a location and you plug it in however you can, copy the data across, and then ship it back.
I think they can export data the same way (at a price), but I have no idea if the same service is available for O365.