There are two available PWM pins specifically for driving LEDs. One is the standard nightlight, D2, on OC2B. You can use the “nightlight” function to dim it– see the “sleep” nightlight mode for an example of how to do this.
The second one is D1, on OC2A. There’s normally no LED here, so if you want to add a signal to drive a big LED, this is a good place to do it. Or, put it at location D2, so you can use the nightlight code directly.