It's not "can you provide the screen DPI to a window?" people bemoan, it's "can you draw one window across two screens with differing DPIs, transparent to the application?"
I have never had a window open across two screens if I could help it. Complete non-problem.
If you have more than one display, and you want to be able to drag windows from one to another and want them to have a similar size after dragging, it's a hard problem.