I think you can also use WinAPI for this. I haven't looked at it yet but I did find this Stack Overflow post:
https://stackoverflow.com/questions/21566307/how-to-get-the-title-bar-height-and-width-for-aero-and-basic-design
Those are for the title bar, which we can get cross-platform via glut. The .h which I'm using is for the taskbar. I'm certain we can do it with QB64 itself, but it'd require a custom data type (RECT structure), and a couple declare library calls, so I just figured, "Heck, if I'm going to have to do that anyway, it's just as easy to just make a .h header," and it grew from there. Originally all I needed was the height of the taskbar, but then width, and finally all 4 coordinates got involved in the process, and my "simple" solution has grown a lot more complicated -- and all just to become obsolete in a few years as WIN 11 doesn't allow for the window to go anywhere but at the bottom of the screen.
With Win11, as long as you know the height, you know all 4 coordinates.
Top = _desktopheight - taskbarheight
Bottom = _desktopheight
Left = 0
Right = _desktopwidth
😁