If you create a void in a family that doesn’t intersect anything, the result will be a free standing void. When you need it to eventually cut an object, you need to move it into position, overlapping with a solid object, you will notice that it doesn’t automatically cut the solid. This is where you need to use the Cut Geometry tool.
Use Cut Geometry Tool, and pick the solid and the void.
If you create a void that intersects the solid objects straight away you will see that the void automatically cuts.
(You can also refer to my previous post about creating the cutting object as a solid first then switching it to a void so that the automatic cutting isn’t activated.)