If you're running Windows then you can disable the case LEDs in an HP Omen computer using the Omen Gaming Hub.
However, there's no equivalent for Linux and no obvious way to permanently disable the LEDs.
When restarting after a shutdown, the LEDs start enabled but if you boot into Windows and, if you've already disabled the LEDs via the Omen Gaming Hub, they will automatically become disabled again as part of Windows starting up. You can then reboot into Linux and they will stay disabled until you next shutdown and restart.
This is hardly ideal - a more permanent and simple approach is to simply unplug the power connector for the LEDs on the motherboard. It's clearly marked "LED":
A little closer (see the two pin connector with red and black wires):
Just unplug this connector and that's it - the LEDs will never bother you again. Note that this will also disable the LED that lights the diamond shape on the front of the case that "breathes" on and off when the computer is sleeping.
Unplugged:
The text on the side of the graphics card, e.g. "RTX 2060" or whatever, is unaffected by this change and there seems to be no way of disabling it. I just covered it with duct tape.
Update: it turns out that, whatever this connector is doing, it is not supplying power - if the LEDs are currently lit and you unplug this connector (while the system is still running) the LEDs stay lit. And it's not an issue where massive capacitors are keeping them lit - I've left it disconnected for some time and the LEDs stay lit. Anyway, if the connector is disconnected and the system is rebooted the LEDs do not light-up - so whatever the mechanics, disconnecting it does what's desired.
