I don’t know if they’re exactly the same but based on my own anecdotal experience the setting to reduce input lag in game optimizer and Nvidia reflex + boost lower input lag significantly and feel roughly the same.
I honestly think you’d be good either way since LG OLEDs including the C2 are known for their incredibly low response times and input lag.
You can find Nvidia Reflex and Reflex + boost in the Diablo IV game settings right where you’d set things like DLSS/DLAA, resolution scale etc… assuming you’re using an Nvidia card that supports it.