WM_SYSCOMMAND works for me (Windows 10, 1909) :
Before MoveWindow :
(mstscInstance.MainWindowHandle is "TscShellContainerClass" class on my OS)
PostMessage(mstscInstance.MainWindowHandle, WM_SYSCOMMAND, SC_RESTORE, IntPtr.Zero);
with :
[DllImport("User32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern int PostMessage(IntPtr hWnd, uint msg, int wParam, IntPtr lParam);
public const int WM_SYSCOMMAND = 0x112;
public const int SC_CLOSE = 0xF060;
public const int SC_RESTORE = 0xF120;