This option controls the number of lines / columns to scroll by when scrolling with a mouse. The option is a comma separated list of parts. Each part consists of a direction and a count as follows: direction:count,direction:count Direction is one of either "hor" or "ver". "hor" controls horizontal scrolling and "ver" controls vertical scrolling. Count sets the amount to scroll by for the given direction, it should be a non negative integer. Each direction should be set at most once. If a direction is omitted, a default value is used (6 for horizontal scrolling and 3 for vertical scrolling). You can disable mouse scrolling by using a count of 0.

Example:

:set mousescroll=ver:5,hor:2

Will make Nvim scroll 5 lines at a time when scrolling vertically, and scroll 2 columns at a time when scrolling horizontally.

(default "ver:3,hor:6")