Change PPT aspect ratio to match Storyline, not the other way around

If the aspect ration is different in PPT and Storyline, change the former to match the latter -- not the other way around, which won't work. Storyline prefers the 4:3 ratio, so you should change your PPT accordingly. Use the "Design" menu item, chose "Screen Size," and select "Ensure fit." Other info about PPT imports here: https://articulate.com/support/article/Storyline-360-Tips-for-Importing-Microsoft-PowerPoint-and-Articulate-Presenter-Content