Implement indentation on a matrix report in Power BI as follows:
Enable Stepped Layout by selecting the matrix visual in the Visualizations pane. In the Format pane under Row Headers, toggle the switch On Stepped Layout, which automatically indents child levels beneath their parent in a hierarchical structure.
Increase the spacing of the space between hierarchical levels for better clarity. This would be an adjustment to whichever suits the kind of visual appeal the report requires.
Highlight fields readably by differentiating the levels or faintly stylizing such as font size, boldness, or color of the parent rows using conditional formatting. You can find this in the Values section of the Fields pane.
With such changes, the matrix report would display hierarchical data clearly, thus making it much easier for the users to interpret relationships between levels.