great instruction! If you'd like to exclude one hand sewing step, you could leave the opening for turning the squares nit on the tip but between corner and tip. It'll be enclosed when folding the corners to the middle. But you seem not to mind some hand sewing 😅
yes, there is a way you can do cathedral windows by machine it is a very different process and has a flatter look. I am not shore if anyone has done a vlog showing this.