I can't regulate body hair length via vertex group in "Trim hair curves" modifier no matter which option I replace with that vertex group. There was no such problem with similar group for a body hair density in "Interpolate hair curves" modifier.
The hair length without vertex group influence
The hair length vertex paint (White-0 Black-0.01 Red-1)
The hair length with a vertex group influence (The length is almost gone)
Blender3.5