The latest update for Power BI desktop breaks the popup modals by not scaling them correctly so most of the content is out of view without being able to scroll. This causes the buttons to be out of view so you cant really use them. 

The problem seems to stem from multi monitor awareness in Power BI. A simple fix was suggested on the investigation thread to switch to system high dpi scaling.

Right click on your Power BI desktop icon in your taskbar and then right click on Power BI Dekstop and select properties.

Click on Change high DPI settings.

On the new screen set High DPI Scaling override to system and your Modals should return to normal after restarting your Power BI desktop instance. 

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