So in the “Smart Lighting”, choose “Turn On & Set Level”. For the trigger select “Switch”, then choose the dimmer you just created.
EDIT - I just tried this with one of my Hue Bulbs… everything works except the Virtual Dimmer. It creates a button to control the group of lights, it only allows for on/off at the set dim level specified in the “Smart Lighting” automation. I’m sure there’s a way to do this… possibly through Trend Setter.