The disk in question is disk04 - a 128 GB SSD drive in an external USB enclosure. I booted the Macbook from a X.11 USB install drive and there was an internal SSD drive as well. a simple fdisk ...
It is easily possible to double the cost of a new M4 Mac mini by buying Apple storage — but if you know what you're doing, you can buy external drives, and save hundreds of dollars by working off ...