Appreciate the advice. Yes it's the latest pixel tablet (not phone)
USB cables: I've several 'good quality' USBC cables and tried them all. One wouldn't 'see' the pixel, I've set that aside. I'm not 100% certain but when I've successfully installed graphene in the past I would have used one of these cables then so I don't believe it's likely that all of my cables are now faulty but I have no obvious way to test to double check? If there is a recommendation or link to a known good cable, I'm happy to purchase and eliminate that as an issue.
Out of disk space: both devices I used have Gbs of free disk space.
One thing that may be relevant that I don't remember having to do in the previous web installer (when I used it successfully) many months ago is that each time the tablet rebooted during the flashing I had to manually click the blue reconnect button (at the end of the progress bar) after each reboot in order for the installer to find the tablet and continue to the next phase.