What should you do first to enable scale-out for a semantic model in Microsoft Power BI?

To enable scale-out for a semantic model in Microsoft Power BI, the first step is to set the Large dataset storage format to On. This setting is crucial because it allows the semantic model to handle larger datasets more efficiently by using a columnar storage format that enhances performance during query execution and data processing.

When the Large dataset storage format is enabled, Power BI can leverage its optimization features, which support more extensive data models and improve scalability. This adjustment allows Power BI to perform better with bigger datasets, thereby enhancing the overall analytical capabilities and responsiveness of reports and dashboards.

Options that involve enabling metrics or data activators, or disabling the large dataset storage format, do not contribute directly to the scale-out capability of the semantic model. These settings have their respective roles but do not serve as the foundational step in preparing for scale-out. Thus, enabling the large dataset storage format is essential for the necessary infrastructure that supports scale-out in the context of Microsoft Power BI.