Figured I'd try to update the old Dell 15" XPS with the broken keyboard as a machine for the kids to use as a desktop (for at-home schooling, etc) and do a bit of testing on the new release while I'm at it. The machine has been on 18.04, was updated and rebooted right before the update, and I did an in-place update to the new LTS with do-release-upgrade to Ubuntu Focal. So far:

• blocked on the postgresql-*-postgis-* packages (they were blacklisted for updates, since the machine isn't my dev machine any more, just removed the packages)
• on completion of the in-place upgrade, the machine hangs on the "Loading initial ramdisk"
• same behaviour booting to a usb-key (after the upgrade)

I've tried a bunch of different kernel and init parameters (there are similar issues people have highlighted around intel micro-code, but the work-arounds don't work here), secure and insecure boot, but so far nothing seems to be able to get to a bootable state. Even old Ubuntu releases no longer seem to be able to boot from USB (but I haven't attempted that in many years on this machine, so no telling if that's a new thing or not)

So for today I think the upgrade is a dead end (for that matter, the machine is just dead in the water until I find something that can boot it). Which is why you use a spare machine for the first upgrade test.

[Update] This was fixed by doing a UEFI update of the BIOS. By creating a Fat32 partition, going to Dell's site, getting the Bios EXE updater, hitting F12 during boot and choosing the EXE file