There seems to be a bug in Unity because ScrollView.mouseWheelScrollSize does affect the ScrollView differently in edit mode and play mode. Tested on Windows 11, Unity 2023.2.3f1.
Brake Floating point number, the deceleration coefficient after scrolling. The value range is 0-1. If set to 1, then the scrolling will stop immediately, if set to 0, then the scrolling will continue ...