if you are using a title less / border less form  or FormBorderStyle.None then your form when maximized will cover the task bar

if you want the title less form to just expand  to working area of the screen and exclude the task bar then you need to set the maximum size of the form like

Me.MaximumSize = Screen.PrimaryScreen.WorkingArea.Size

also this will work for primary screen will not work in dual screen setup