SCNAction.move(to:SCNVector3)
doesn't work. It moves the shape but the shape doesn't fall.
There's some other action?
If you haven't already, you'll need to give your SCNNode a physicsBody and configure it prior to adding the node to the scene.
let body = SCNPhysicsBody(type: SCNPhysicsBodyType, shape: SCNPhysicsShape)
myNode.physicsBody = body
Then you can set the .isAffectedByGravity property to true.
myNode.physicsBody?.isAffectedByGravity = true
Now, when you add the node to the scene, it will fall.