据我所知，你有这些要求：

• Control-F组合键创建新窗体
• 无论当前哪个窗体（或控件）具有焦点，热键都应该仍然有效。
• 热键是应用程序本地的。

实现IMessageFilter应该能够有效地实现以下目标：

public partial class MainForm : Form, IMessageFilter
{
    public MainForm()
    {
        InitializeComponent();
        Application.AddMessageFilter(this);
        Disposed += (sender, e) =>Application.RemoveMessageFilter(this);
    }
    const int WM_KEYDOWN = 0x0100;
    public bool PreFilterMessage(ref Message m)
    {
        switch (m.Msg)
        {
            case WM_KEYDOWN:
                switch((Keys)m.WParam | ModifierKeys)
                {
                    case Keys.Control | Keys.F:
                        onNewForm();
                        break;
                }
                break;
        }
        return false;
    }

    int _count = 0;
    private void onNewForm()
    {
        char c = (char)(_count + 'A');
        int dim = ++_count * SystemInformation.CaptionHeight;
        new TextBoxForm
        {
            Name = $"textBoxForm{c}",
            Text = $"TextBoxForm {c}",
            Size = this.Size,
            StartPosition= FormStartPosition.Manual,
            Location = new Point(Left + dim, Top + dim),
        }.Show(this);
    }
}