How do I make backlights to go out when I press the FN key?

Honestly, I am not 100% sure, but you can go into the synapse 3 beta application and I think you can go into Macros and/or Nano Leaf, I forgot which one, anyways I am pretty sure it is Macros its one of the individual applications within Synapse 3 beta, and you should be able to determine, find, see, and even change the function of most keys, but at least or at the least the application will be able to tell/show which keycap goes to or is in charge of which function/action!

Hi, thanks a lot..I already have Synapse 3, couldn't see any setting that would "switch on/off" whether (and which) F keys are lighting up when one presses the Fn key...maybe it's related to specific models but need to see or someone else to add a post... Thanks a lot.

You might or the keyboard that you have might have the FN key as a function key maybe it is the chroma light on/off switch look throughout your SYNAPSE 3 BETA APPLICATION, make sure your look through the chroma connect, chroma studios, and etc..., if you go through all the modules and your specific connected software and devices then you should find exactly why it is the FN key is turning off the chroma lights when you press it! Does the chroma lights on the keyboard comeback on by pressing the FN key for a second time after the first press/push turns them off, does the FN key then on the second press turn them back on? I hope this provides some assistance or at least some help to where you can solve the issue!