Hi @nanci ,
Could you please share a bit more about the issue that you mentioned?
Could you please show more details about the "Large" Power BI tile that you mentioned?
Have you taken a try to create a Tablet layout app to diaplay your Power BI tile?
Please consider create a Tablet layout canvas app using PowerApps, then add a Power BI tile within the screen, make the Power BI tile control expand to the whole screen. Then connect the Power BI tile control to your Power BI "Large" tile, check if the issue is solved.
Currently, the Scrolling bar functionality is not supported within Power BI tile control in PowerApps. If you want to display a large Power BI tile which could only be displayed partly within a Phone layout app or Tablet layout app, I afraid that there is no way to achieve your needs in PowerApps.
If you would like this feature to be added in PowerApps, please submit an idea to PowerApps Ideas Fourm:
https://powerusers.microsoft.com/t5/PowerApps-Ideas/idb-p/PowerAppsIdeas
Best regards,