First question - is the Z axis motor controlled by your controller? Many machines have up/down buttons that control a DC motor. If your machine works this way, LightBurn will not be able to drive the Z.
Are you able to jog the Z with the up/down buttons in LightBurn? If so, you should be able to move the Z with the pass steps. Which version of LightBurn are you using?
I Just installed the newest Software ( 0.9.02) and can jog the Z-axis with the software.
Before i Had 0.8.5 i think but didnt Test moving z with Software.
But it IS also not working. It follows the shape x-times, but without moving the bed.
Number of passes : 3
Z step per Pass 3.00 mm
Z-axis enabled in settings
Relative Z moves only ist disabled (also not working when enabled)
I tried Focus Z and without Focus. When its focused i can only lower the bed (away from Laser), but not into the Laser.
Have you enabled the Z control in the device settings in LightBurn? If not, you can jog the Z, but the software will not emit commands to move it during the job.