Will not find my Atomstack as machine

In LightBurn, in the Laser window, click the Devices button and check to see if it is there, powered and communicating. On your Mac, if you have the driver, you may see wch in the name of one of the device options. That will be the one you want.
If you do not see an option for it, you may have another program that is connected to it and has taken over the USB port.
If this is the first attempt to communicate with the Atomstack engraver you likely need the CH340 driver.