该菜单被称为“窗口系统菜单”。它可以通过GetSystemMenu检索。它将返回一个 Menu 对象的句柄。
获取菜单句柄后，可以将其传递给ModifyMenu函数以修改其中的菜单项。它需要修改哪些菜单项。您可以使用uPosition参数来给予它。你可以给予一个相对位置，它是从零开始的索引或标识符。系统菜单包含具有预定义标识符的菜单项。它们是SC_MINIMIZE、SC_MAXIMIZE、SC_CLOSE等。您可以使用这些标识符来引用要修改的菜单项。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    private IntPtr _hwnd = IntPtr.Zero; 
    protected override void OnInitialized(EventArgs e)
    {
        base.OnInitialized(e);
        _hwnd = new WindowInteropHelper(this).EnsureHandle();
        IntPtr hSystemMenu = GetSystemMenu(_hwnd, false);
        StringBuilder buffer = new StringBuilder(64);
        int[] itemIDs = new int[2] { SC_MAXIMIZE, SC_MINIMIZE };
        foreach (var itemID in itemIDs)
        {
            buffer.Clear();
            GetMenuString(hSystemMenu, itemID, buffer, 64, MF_BYCOMMAND);
            ModifyMenu(hSystemMenu, itemID, MF_BYCOMMAND | MF_GRAYED, 0, buffer.ToString());
        }
    }
    
    private const int SC_MAXIMIZE = 0xF030;
    private const int SC_MINIMIZE = 0xF020;
    private const int MF_DISABLED = 0x00000002;
    private const int MF_ENABLED = 0x00000000;
    private const int MF_BYCOMMAND = 0x00000000;
    private const int MF_GRAYED = 0x00000001;

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern bool ModifyMenu(IntPtr hMenu, int uPosition, int uFlags, int uIDNewItem, string lpNewItem);
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern int GetMenuString(IntPtr hMenu, int uIDItem, [Out] StringBuilder lpString, int cchMax, int flags);
}