How did I fix «Error response from daemon: cgroups: cannot find cgroup mount destination: unknown» for Docker after switching Debian 10 from SysVinit to Systemd?

mkdir /sys/fs/cgroup/systemd
mount -t cgroup -o none,name=systemd cgroup /sys/fs/cgroup/systemd

The best solution seems to be to upgrade Docker:

How did I upgrade Docker Client from 19 to 24 on Debian 10?