The StartPosition attribute has the following options, which have the following meanings:
The CenterParent form is centered in its parent form.
The CenterScreen form is centered in the current display window, and its size is specified in the form size.
The location of the Manual form is determined by the
WindowsDefaultBounds The window is positioned in the default position of
WindowsDefaultLocation The window is positioned at the default position in
CenterScreen does not mean that the screen is centered (it is relative), it is centered in the "current display window".
When using the Show() method, you should select CenterScreen,
When using the ShowDialog() method, you should select CenterParent, so that the window to be displayed can be centered.