Yes there are settings.
1. It’s the viewport size. If it’s set to 7, then the scrollbar will only appear if there are 8 or more results. The initial value is 4. You can change this setting on the General Option -> Behavior -> Results box viewport (in item numbers) option.
2. It’s adjustable just under the previous setting: General Option -> Behavior -> Max. results option.
If the Max results count is bigget than the viewport, the scrollbar is displayed.Best,
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