What do you mean? It's been there for years: https://packages.debian.org/docker.io
It’s an old version, and I think it isn’t supported by Docker Inc (for the reasons mentioned in the sibling comment), but it’s there.
Damn good to know! Have been gaslit by the ever-changing docker install instructions. Of course it would be a lagging version, but I think the docker feature-set has converged years ago, why would I care any more about the docker version than e.g. about the version of grep?