You are having that problem because the docked alias is using port 3000. You should be able to open multiple consoles using the command without specifying a port:
docker run --rm -it -v ${PWD}:/rails -v ruby-bundle-cache:/bundle ghcr.io/rails/cli rails console
In addition, you could add this alias to avoid the command above:
alias rails-console='docker run --rm -it -v ${PWD}:/rails -v ruby-bundle-cache:/bundle ghcr.io/rails/cli rails console'

ah that makes sense!

perhaps the README suggestion for the docked alias should not include -p 3000:3000 since it is only really useful for server and bin/dev CLI commands.

Why do you need to run multiple consoles?

I have multiple consoles running b/c I'm debugging different things in the application. It helps to have the related history of commands within a single console.

Another option would be to get into running container. I start with docked rails server, then I get list of running containers docker ps to find name of the running container and by docker exec -it <container_name> rails c. You can do it in as many terminals as needed.