OpenLayers print preview

I’m trying to accomplish something similar to what you have in Google Earth, if you print the map.
You have an area, where you can see what you will get on the paper when you print, which have the right aspect ratio according to the DIN-Format.

I checked the OpenLayers example how to print from here https://openlayers.org/en/latest/examples/export-pdf.html.

But you actually don’t get what you see, depend on the DPI I choose I can see map sections beyond the viewport.

What should I keep in mind if I want to implement this feature?