Root cause, as best I can tell, is containers/automation_images#115. This was supposed to make ubuntu use runc, but it didn't. ubuntu is using crun. Confirmation: #13376 brought in those new VM images, but the ubuntu sys log clearly shows:

[+0006s] # Arch:amd64 OS:ubuntu21.10 Runtime:crun Rootless:false Events:journald Logdriver:journald Cgroups:v2+systemd Net:cni
                                             ^^^^

Solution is going to require a VM dance, and some way to actually log in to ubuntu to confirm, so it's not something I can do. It will have to wait for @cevich's return.