The problem

Fedora doesn’t support the sysfs GPIO interface, and since it isn’t running the official raspbian kernel, you can’t use the GPU driver as listed on the RPi forums.

What I tried first

At first I tried enabling the configuration options in /boot/efi/config.txt, but this had no effect, presumably due to the switch of the LEDs to the GPIO expander.

Enabling GPIO

Since the LED is on a GPIO extender, I wondered if Fedora would be able to see it via the GPIO. First follow to install libgpiod, and run sudo gpioinfo. At the end you should see this output:

gpiochip1 - 8 lines:
	line   0:      "BT_ON"   "shutdown"  output  active-high [used]
	line   1:      "WL_ON"      "reset"  output   active-low [used]
	line   2: "STATUS_LED"        "ACT"  output  active-high [used]
	line   3:    "LAN_RUN"       unused  output  active-high 
	line   4: "HDMI_HPD_N"       unused   input  active-high 
	line   5:  "CAM_GPIO0"       unused  output  active-high 
	line   6:  "CAM_GPIO1"       unused  output  active-high 
	line   7:  "PWR_LOW_N"       unused   input  active-high 

Success! On line 7 you see the power LED.

Turning off the LED

It’s as simple as setting that pin to 1 - sudo gpioset gpiochip1 7=1 will turn off the LED.