I’m making the assumption that you’ve upgraded from 20.04.x LTS.
I will be going through a test upgrade in a local VM tomorrow, I suspect the key will be to repeat Set up the repository step 3, i.e. updating /etc/apt/sources.list.d/docker.list to use jammy rather than focal, followed by apt-get update && apt-get upgrade to bring the packages up to date with the new source list.
You’ve already solved your issue but for anyone else that finds their way here, I’ll report back afterwards as to whether this works in the way I expect or what extra steps are required.