X11 Forwarding with my Entire Screen
This isn't how X11 works on the Mac currently (or at any time in the past).

The native Mac window manager uses Quartz 2D and Core Graphics to accomplish the rendering and composting of windows and icons on the Mac screen.

X11 writes into that space as a consumer - not as the end-all provider of drawing services so it can't forward things it doesn't get to see.

You will want to set up VNC sharing (which is the native Mac screen sharing technology) if you can't get by with just forwarding the X11 graphics.