Full automatic scrolling option

Here is the option setting:

And here is the scrollbar in the treeview that I am not expecting to see:

Any advice or insight would be greatly appreciated, as always!

The Horizontal scrolling style options only change how horizontal (left/right) scrolling behaves in the tree, with options to mimic the way horizontal scrolling worked in File Explorer's tree in various versions of Windows.

The vertical (up/down) scrollbar is always visible (unless all the items fit on screen) and not affected by those options.