Transfer iMac 2012 to mini4

Hi everyone,

I've been lucky enough to buy a new Mac mini 4.

I'm trying to transfer my data from an iMac 2012 so I'm waiting for my thunderbolt 3 (usb-c) to thunderbolt 2 adapter

For some reason mini 4 isn't seeing any of my external usb HDs

I've just formatted my new SSD drive on the mini4 and it's visible.

I've activated in general settings see all disks