This brush can only affect assets that were added in the current Layout node.
When moving in screen space, you can easily move assets off the ground plane if you're not working in an orthographic view (the brush does not automatically snap to the XZ plane or construction plane or anything like that). If the input has a “ground” surface, you can turn on Snap to geometry to keep the assets snapped to the ground.
Radius of the nudge brush.
Snap To Geometry
Snap the nudged assets to geometry controlled by the Mode parameter below: the input geometry (usually the ground), existing assets placed by the current Layout node, or both.
When Snap To Geometry is on, whether the assets should snap to the input geometry (usually the ground), existing assets placed by the current Layout node, or both.