Every other image I have tried for the Raspberry Pi works by adding a blank file called ssh to the boot partition before booting the Pi for the first time, except for this one. I don't understand why this one doesn't work?
As a result, I have had to use the Ubuntu server 20.04 image, which booted just fine, and then tried loading the Mate desktop. Unfortunately, doing it this way means that I get the bare minimum desktop rather than the fully featured version which I was hoping for from the Mate image.