The best option for an analyst who wants to run a single action on an event is to open the event and run the action directly from the Investigation View. The Investigation View allows users to interact with events directly, and provides the ability to execute specific actions without the need for playbook development or debugging. This is the most straightforward and efficient way to execute a single action on an event, without the overhead of creating or editing playbooks.

While creating a playbook and using the Playbook Debugger are viable options, they introduce unnecessary complexity for running just one action. The goal is to allow the analyst to act quickly and efficiently within the Investigation View.

Splunk SOAR Documentation: Investigation View Overview.

Splunk SOAR Best Practices for Running Actions on Events.