The SerialAgent requires the serialPort attribute to be specified and this should be the device path but you need to remember you are running through docker and I don’t know what mac is like for accessing USB devices from within docker; you can often resort to host mode which generally gives docker direct access to the host.
Your agent status should show as connected if it has successfully managed to establish a connection.
Once you have a connection then you can use the agentLink configuration item to link attributes to the agent specifying what data needs to be sent and how to parse received data and associate it with the different attributes. These generic agents can require quite some configuration for this reason and if you can write some java you could try writing an agent (a programmatic solution rather than a declarative one).