How to make the correct display of the slider in the ScrollView?

Question

Qt

The ScrollView contains a ListView containing categories with subcategories. When you click on a category, a list with subcategories expands. While the expanded list is in the screen area, everything is fine, but if there are more subcategories, then the slider changes size as it scrolls. Starting from the smallest while we are at the beginning of the list of subcategories and up to the size when all categories are collapsed. How can this nonsense be defeated? As I understand it, the scroll calculates only part of the area, which is why the size of the slider changes.
ScrollView Code

Answer 1

In general, I took this scroll and added one function to it, into which the height of the content is passed. Inside the scroll, not flickable.contentHeight is used, but my value. Now everything works correctly

Answer 2

ScrollView contains ListView

Is this investment really necessary? How is the list with subcategories implemented?