Ruida will initialize Z upon powering on / homing to 3000mm. Auto focus will set Z to 0mm. You cannot move Z up (inward) from 0 (not through LightBurn or from your Ruida HMI). You can move Z down (outward) from 0. None of this will affect LightBurn’s functionality for Z on your controller.
If you intend to raise Z after you have set the focus with auto focus, then you will need to reset the controller and allow X and Y to re-home and Z to be reset to Ruida’s arbitrary 3000mm (and your Z will be at your focused height).
Within LightBurn, can you verify that you have enabled Z Axis Control:
@LightBurn: I just observed that when Z is focused / set to 0, if a layer is set to offset Z inward then the layer will run (without moving Z) and lower Z when it is finished (as if it had been raised).