Responsive design is fundamentally different

In web, one layout system reflows from desktop to tablet to mobile. Power BI works with a configured report canvas — page settings offer fixed aspect ratios such as 16:9, 4:3 and custom dimensions — and handles phones through a separate mobile-optimized layout in which existing visuals are selected and rearranged.

DESKTOP COMPOSITION        MOBILE COMPOSITION
Header                     Key filter
Filters                    KPI
KPIs                       KPI
Chart + breakdown          Primary chart
Table                      Exception list

Not:

Desktop layout
   ↓ magically shrinks ↓
Mobile

Microsoft recommends reducing content on mobile, prioritizing the important visuals and organizing the page top-to-bottom.