Test alternative PointToScreen and ScreenToPoint methods.

WindowHelper.cs

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Interop;
using System.Windows.Media;

public static class WindowHelper
{
    public static Point PointToScreen(Visual visual, Point point)
    {
        if (PresentationSource.FromVisual(visual) is HwndSource source)
        {
            var dpi = VisualTreeHelper.GetDpi(visual);

            var buffer = new POINT
            {
                x = (int)(point.X * dpi.DpiScaleX),
                y = (int)(point.Y * dpi.DpiScaleY)
            };

            if (ClientToScreen(source.Handle, ref buffer))
                return buffer;
        }
        return default;
    }

    public static Point ScreenToPoint(Visual visual, Point point)
    {
        if (PresentationSource.FromVisual(visual) is HwndSource source)
        {
            POINT buffer = point;
            if (ScreenToClient(source.Handle, ref buffer))
            {
                var dpi = VisualTreeHelper.GetDpi(visual);

                return new Point
                {
                    X = (int)(buffer.x / dpi.DpiScaleX),
                    Y = (int)(buffer.y / dpi.DpiScaleY)
                };
            }
        }
        return default;
    }

    public static Point GetCursorPoint()
    {
        return GetCursorPos(out POINT point) ? point : default;
    }

    #region Win32

    [DllImport("User32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool ClientToScreen(
        IntPtr hWnd,
        ref POINT lpPoint);

    [DllImport("User32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool ScreenToClient(
        IntPtr hWnd,
        ref POINT lpPoint);

    [DllImport("User32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetCursorPos(
        out POINT lpPoint);

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int x;
        public int y;

        public POINT(int x, int y) => (this.x, this.y) = (x, y);

        public static implicit operator Point(POINT point) => new Point(point.x, point.y);
        public static implicit operator POINT(Point point) => new POINT((int)point.X, (int)point.Y);
    }

    #endregion
}