Can't import .GC or .Gcode file

I can open .gc file with notepad and edit. Then run with Lightburn that way right. I want to test some codes to see if they work.
Is there a list of accepted codes grbl reads and runs somewhere that you know of. I’ve done CNC programming for 42 years and want to test work arounds for CNC code not read.
Thanks for the run gcode button hint, didn’t even notice it.