and scroll through it with the mouse wheel, the toplevel frame also scrolls. How can I disable the mouse wheel scrolling in the toplevel frame when the focus is in a listbox?

Well :) don't bind to all, bind to something else, like $frame

Or filter the events you get, ignore based on the tk variables $Tk::event and $Tk::widget ... for example, don't scroll if $Tk::widget is not $topframe

Or try Tk::DynaMouseWheelBind ...