The GRBL doc:
The list of supported G-Codes is at the bottom of that page.
The “standards-compliant g-code” they talk about behaves according to the LinuxCNC doc:
https://linuxcnc.org/docs/stable/html/
However, AFAICT, desktop laser manufacturers start with that code, make their own changes, ignore GRBL’s GPL licensing, keep their source code secret, and figure you don’t care about the details they’re not telling you about. So you’ll surely come across G-Code commands that don’t behave the way any doc suggests they will or, in some cases, don’t work at all.
And you definitely should run the most recent LightBurn version, because then I won’t feel so bad about missing the LightBurn 1.1.04 in that screenshot. 