Would you be willing to publish your C# code that deals with reading window information?
I'm also working on a desktop pet project (in 3.2.1 before they reworked window transparency clickthrough) and would love the ability to read window position data! Anything beyond GDscript is outside of my wheelhouse of expertise.
Here's the C# code that interacts with the Windows APIs: https://gist.github.com/RachelfTech/d98a7c8f4c7eb8bb18a09552cf7bab40
Then you can reference https://docs.godotengine.org/en/stable/tutorials/scripting/cross_language_script... to interact with the data from C#.
Just wanted to note that the file is a bit messy (I didn't end up using all the code for the final project) and I also don't really know C#, but hope it helps anyway!
