Yes, that restarted the container, but without any upgrade.
I don’t know what happens next after database system is ready to accept connections in the upgrade process, but that’s as far as it gets and then never any further (unless the next step takes a very long time).
Yes, Ubuntu has been updated previously. So Docker is on aufs, always has been.
Is it possible to rebuild without upgrading? If that works, then possibly I can get the current Docker switched from aufs to overlay2, which would then mean potentially I can upgrade Ubunto to 22, which might mean that other things then work - but at the moment I have no idea why the upgrade stalls at that point, so it’s pretty much just hope as to what might resolve it.