Hi again, and thanks again for your help here. I was a bit busy yesterday evening, but I ordered a couple of usb-c to usb-a converters, which arrived today, and once home I had another go. To be precise, I repartitioned the sd card, as suggested, with an LVM planetlinux partition (102GB) and a small vfat partition for Android (18GB), but I left the config and linux files on the usb stick and plugged that in via the usb converter instead of the planet adapter.
Certainly, I think it went further today. Some three hours after I rebooted with the silver button held down, the Debian swoosh is still visible, along with the message, 'Gemian booting - /dev/planetlinux/gemian'. Does this mean that it completed the copying/installing and is trying (but failing?) to boot? Or do I now need to hold escape to turn it off and force a reboot? Just wanted to check, as 3 hours seems to be a bit longer than you were expecting it to take. I didn't take note of the initial message and haven't watched it for all 3 hours, so I'm not sure if it is giving the same message as when it started, or whether there was an intermediate message saying something along the lines of 'copying' or 'installing'.
Anyway, I thought I'd feedback. I have to go out now, but will plug it in and see whether it has changed at all when I get back in another couple of hours (which will be a full five hours or more since I started it off with the reboot).
Thanks for any thoughts you have. And thanks for all your work on this!
All the best,
Ian