Have you downloaded the Genealogy Treehttps://gramps-project.org/wiki/index.php/Addon:GenealogyTree#Descendant_tree add-on and tried that?
Here’s one of the graphs it offers - the sand lock tree. It is similar to the diagram in your link. However, it does not have couples combined in a single box. (Do you have an example of 2 people in one box in a pedigree-style diagram? That is not a layout I’ve seen anywhere. Although I have seen boxes for 2 people share a common edge.)
If you have not yet tried downloading add-ons, please start. Gramps is a fairly extensive basic starter kit … but the accessories are what makes it great. And they are still free. (So this ain’t an “up-sell”.)