If you create a family and you want the height to be an instance parameter that has a Grip arrow visible to adjust it in your project file. It isn’t as obvious as you think.
When you create the family and assign the Height Instance Parameter. You have to make sure that you dimension from the Reference Plane not the Reference Level.
If you dimension from the Reference Level you won’t get the little Grip Arrows.
As standard practice when creating Families, I always dimension to Reference Planes.