Constant/variable power

You’re setup as GRBL-M3, not GRBL. Edit the Device and select GRBL and then complete the wizard. You should then have Constant Power mode as an option.

Note that with GRBL-M3 you’re basically always in Constant Power mode so you won’t get different results by enabling that from what you’re currently getting. However, you should get better results on non-Constant Power burns.

On or off is immaterial as you’re changing the device profile that LightBurn uses when communicating to the laser. Either approach will work.