The tuning item selection window does not allow resizing and the vertical scroll bar disappears as soon as you move the window. In practice with a laptop with 1366x768 screen resolution, you can’t select the bottom items.
Could resizing and scroll bars be added for future versions of Mission Planner?
Yes, that happens and it is a mesh. At home I have a 1920x1080 additional external monitor connected through a docking station, so I move the window to it and eventually (don’t remember how) can see all items.