In the appstore there is a widget for a graph which will generate a png file of that graph so you can use it in a document template: https://appstore.home.mendix.com/link/app/3011/TimeSeries/JFree-Charts-(.png-images)
Other option would be to use something like Templater: https://appstore.home.mendix.com/link/app/109927/Daywize/TemplaterForMendix
This way you can have an Excel template with the graph and use tokens to refresh the data in Excel that produces the graph.
Regards,
Ronald