There is no auth needed for gh runners? Like a secret shared between them and the repo? I would guess repo secrets are not shared when forked… right?

Not sure what Disk Manager is, but if it says

USB Mass Storage device detected

It appears to be something. If you do a sudo journalctl -f before you plug it in, does it tell you what device name it is given? If it is sata-to-usb you are using it is probably /dev/sd[a-z] or so, does anyone show up when you plug it in?