Minecraft wiki entry for Development_versions, associated text: Sensitivity, invert mouse and touchscreen mode have been moved to a subsection "mouse settings".
Added new options scroll sensitivity and discrete scrolling, also in "mouse settings"; these fix MC-123773.
Scroll sensitivity is a multiplier for scroll magnitude; the setting was first added in 18w21a but was only accessible by editing mouseWheelSensitivity in options.txt.
Discrete scrolling tells the game to ignore scroll magnitude values given by the operating system and instead to act as if the operating system supplied −1 or +1. These will be influenced by the sensitivity afterward if needed.
If unwanted scrolling occurs, enable discrete scrolling and set the sensitivity to 1.