Docker image exists, but "docker run" doesn't find it

If you do not specify which version of zcgzcgzcg/squadv2 you want, Docker will, per default use the tag latest.

But you don't have any image zcgzcgzcg/squadv2:latest.
You have one tagged 4.0, though, so:

docker run zcgzcgzcg/squadv2:4.0

Is what you are looking for.

This is implicitly described in the documentation where they point at the fact that:

$ docker run --name test -it debian

This example runs a container named test using the debian:latest image.

^{Source: https://docs.docker.com/engine/reference/commandline/run/#assign-name-and-allocate-pseudo-tty---name--it}

But it is also explicitly descriped in the docker pull page:

If no tag is provided, Docker Engine uses the :latest tag as a default.

^{Source: https://docs.docker.com/engine/reference/commandline/pull/#pull-an-image-from-docker-hub}

The problem is you are not specifying the tag in your docker run command. You have pulled 4.0, as you can see in the docker images output - but when you don't specify the tag, it will default to latest - which you don't have. So, try this:

docker run zcgzcgzcg/squadv2:4.0