Hi Reinout,
Unforunately, mendix imposes limitations on where you can place scroll containers (I am sure it is for a good reason).
Did you try what happens if you add the scroll yourself with css.
Put the following code on your listview under style:
overflow-y: scroll;
max-height: 100vh;
This will assure that the scroll bar is always visible (it will be disbled if the content fits vertically) and that the container will not be bigger than the screen.
Hope this helps,
Andrej