Trying to get things straight

I’ve proably missed something fundamental, just trying to do draw 90° lines with some form of control aligning not only the rectangles but also the actual lines… Please check this quick video and let me know what I’m doing wrong :-)

It looks like you started with a straight line and added a midpoint. Use instead an orthogonal connector. (Line type is set in the leftmost pulldown in the Lines inspector.) There’s a handle on the line for controlling where the line breaks. It’s still something of a chore to keep lines the way you want them; dealing with OG’s line routing algorithm is something of an adventure. You may have to reset the line path almost every time you move one of the shapes, but at least the line segments remain orthogonal.