What must be done to validate multiple stories in one action?

To validate multiple stories in one action, selecting the option to "Create Deployment" and choosing "Validation Only" is the correct approach. This method allows users to efficiently verify all selected stories collectively without needing to merge them into a single deployment or validate each story one-by-one.

This option is particularly advantageous in managing workflow and maintaining efficiency, especially in environments where multiple stories require simultaneous validation. By using this method, users can ensure that all stories are compliant with the necessary criteria in one streamlined process, which simplifies project management and accelerates the development cycle.

The other options involve processes that add complexity or require more effort. Merging all stories into one deployment would not be an efficient way to validate and could lead to complications if issues are identified within the deployment. Individually validating each story can be time-consuming, and creating separate validation branches for each story may complicate version control, leading to a less organized workflow. Thus, using the "Validation Only" deployment is a more effective and efficient technique for validating multiple stories in just one action.