Which Power BI interface should you use to view and modify all the steps in M code?

The Advanced Editor in Power Query Editor is the appropriate interface for viewing and modifying all the steps in M code. This tool provides a comprehensive view of the query's code, which is essential for any data transformation and query adjustments.

When utilizing the Advanced Editor, you can see the entire M code, including each transformation step applied to the data as well as any custom functions or filters you may have implemented. This level of detail enables users to understand the sequence of data transformations and make precise adjustments to optimize queries or correct errors.

In contrast, other interfaces do not provide the detailed breakdown needed for modifying the underlying M code. The Data view showcases the data itself but does not allow for modifications to the query steps directly. The Formula Bar can display individual inline expressions, but it is limited to the current step and does not give an overview of the entire query. Lastly, the Model view is used for managing relationships and visualizing data models rather than manipulating query code. Thus, the Advanced Editor is the go-to option for those needing to interact deeply with M code within Power BI.