The state: operator can be used with either a Workflow Name (which is a text search on workflow state names) or a Workflow ID.
If you use the Workflow ID, note that it is Team-specific, meaning it will return results only for Stories in a specific team (even if the text-based State name, ex. Unscheduled, is the same across Teams).
In the example below, 500000016 is the Workflow ID for the Unscheduled State in one Team in this Workspace.
If you use the Workflow Name with the operator, state:Unscheduled, it will search across Teams based on the text of the name. You can see that in addition to the search results returned using 500000016, using the name Unscheduled returns results from all Teams in the Workspace.
In addition to the state: operator, the following operators search across the different types of workflow states.
Since stories can only have one workflow state, using more than one of these operators can yield no results.