Which tool is essential for modifying data before visualization in Power BI?

The option "Transform Data" is essential for modifying data before visualization in Power BI because it directs users to the Power Query Editor, a powerful tool that allows for the extraction, transformation, and loading (ETL) of data. Within this editor, users can clean and reshape their data by applying various transformations, such as removing duplicates, filtering rows, pivoting or unpivoting columns, and merging datasets. This preprocessing step ensures that the data is in the right structure and format for effective analysis and visualization in Power BI dashboards and reports.

The other options do not serve this primary purpose. Narratives are useful for enriching reports but do not modify the underlying data. Embed Code pertains to integrating Power BI reports into applications or websites. Data Link allows connections to various data sources but lacks the functionality of transforming data within Power BI itself.