There was another recent post hoping for something similar:
I personally wouldn’t mind having something like this as well as a way of setting both the start end end of the g-code save feature.
There are a number of feature requests that already cover similar functionality. I suggest you check those out and vote for those accordingly.
Some that I found:
See Gcode before cutting · LightBurn (fider.io)
save / resume or restart from a particular point in the stream / gcode file · LightBurn (fider.io)