Apologies for this delayed response. To assist, below I share how this button is designed to behave.
Press the button to turn on the laser, and press it again to turn it off. Set the Power value to a very low value that makes the laser just visible enough to see and focus. Too bright and you run the risk of burning the material when your focus is correct.
Most likely that is a safety feature in the firmware of the laser itself, and not something that LightBurn would be able to control. I would suggest contacting AtomStack to see if there is a way to override this.