The doc says

Make sure you have both docker and docker-compose(>=1.24.0) installed. On Ubuntu, just run apt install docker-compose docker.io.

and I have,

$ docker-compose -v
docker-compose version 1.25.0, build unknown

However, I don’t have docker.io, because

The following packages have unmet dependencies:
 containerd.io : Conflicts: containerd
                 Conflicts: runc
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.

I am a bit wary about uninstalling containerd and runc, because I have a few other docker containers running on the VPS and I don’t want to break them. What is the difference between docker.io and the regular docker package? Is it why docker-compose throws an error?

I run my own Mastodon instance, but I haven’t been able to configure a lemmy instance. The readme is not currently as user-friendly as the one for Mastodon. I will try again sometime later if it’s improved.