My embedded report has unwanted margins which is filled with the report 'wallpaper'. The report and iFrame have identical frame size and the report is set to render without borders using powerbi.js.
The issue seems to be related to the 'page view' settings in PBI desktop.
Full detail and workaround here:
Additional info: possibly also related to/affected by the 'modern visual header' setting under current file/visual options
Please create a support ticket to let engineers look into the issue on your side.
Best Regards,Qiuyun Yu