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?"
You can absolutely do that on X11, but you have to do it in the client, and no one cares to do it.
if you have to do it in the client, aka the application, then it's not transparent to the application
If we can require applications to draw their own window controls, I think we can ask them to handle their pixel densities.