I don’t recommend grbl version 1.1f for laser users due to the changes it makes in the way G-code commands work. I prefer this version if you don’t require spindle speed and feed rate overrides., but you can get 1.1f working if you read this document and follow the changes.
For my version of grbl use these settings for laser mode:
$30=255. (rpm max) ************* This value can be anything for grbl 1.1f
$31=0. (rpm min)
$32=1 (laser mode, bool)
Here is a good way to handle spindle/laser selection. Change D11 to PWM output for the X-controller and use GND beside it for the Arduino ground.
