Thanks, images:ubuntu/20.04 indeed doesn’t have this issue. I will need to get to grips with the differences though:
root@tst1:~# dpkg-query -l | wc -l
248
root@tst2:~# dpkg-query -l | wc -l
568
It looks like images:ubuntu/20.04 is only ubuntu-minimal, while ubuntu:20.04 has ubuntu-server and ubuntu-standard.
This gives a major problem for me: images:ubuntu/20.04 doesn’t have cloud-init, which means that my scripted container creation doesn’t work (I’ve tested it). The other things which are missing, like openssh-server, I could add easily if cloud-init were installed.