Atomic contains the Cockpit Bridge process, but not the Webservice. This means you can add an Atomic host to another Cockpit dashboard, but not connect to it directly.
If you want to connect directly to your Atomic Host with your web browser, use this privileged container.
Run it like so:
# atomic run stefwalter/cockpit-ws
And then use your web browser to log into port 9090 on your host IP address as usual.
Important: This expects that Atomic (the host operating system) has the cockpit-bridge executable and cockpit-shell package.