Gdk_Monitor not found in Adacore version of GtkAda for Windows

I am trying to wite a GtkAda program that is Hardware independent. One of the things I have to do is setting a correct Window size.
As I myself have screen of 3840 * 2160 pixels and the graphical card has an even larger possibility. For that program a default size of 2000 * 1200 is a reasonable size. running that program on another system (same screen, card has a maximim size of 1920 * 1080) the window is to large for the screen and cannot be moved anymore.
I want a procedure/function the returns the minimum of the screen size and the size allowed by the graphical card, on the first machine 3840 * 2160 (screen size) and on the second 1920 * 1080 (graphical card).
On internet I found Gdk_Screen where all the promissing routines were depreciated and Gdk_Monitor which could not be reached in my windows version (Adacore 2020). I donot know if it can be reached in the Linux version.
What is my solution

Start by checking the Adacore 2020 GtkAda Windows bindings for Gdk_Screen and Gdk_Monitor, comparing their availability with the Linux version if possible. The issue is resolved when a supported way to determine the usable screen or graphics-card size on Windows is identified and documented.