I too would like a straight forward explanation, I have Google Drive files that when i try to use the EMBED Iframe or EMBED svg, I place that code generated into the wiki page, but it is not interpreted as a diagram.
I have tried the various other methods described in the documenation and have
draw.io app installed on the github.
It seems that to have a live diagram, there is a lot of programatic things that you have to do to make it happen which is more cumbersome than just dropping a new SVG into the wiki every time i change the diagram.
dave