LightBurn 1.04 (and 1.01, 1.02, 1.03) Linux64-Mint 20.02 UMA on a Dell latitude D630
to reproduce:
If you start LightBurn before connecting serial device /dev/ttyUSB* ,then it will not show in the device list unless app is restarted while the device is present.
If you dis/reconnected (or reset the GRBL), and it enumerates as /dev/ttyUSB1 instead of “0”, you will still see ttyUSB0 in the device list, but not ttyUSB1
(sorry Andrek, I copy your text since it is the same problem)
Same as issue from Andrek on Dec 19, 2019
Once it is connected: nothing to say but 