I wanted to go RGB free when I built my desktop, but ran into the exact issue you describe. I kinda just shrugged and accepted it, but maybe I should have looked more deeply into their configurability. Off or all white would be a much better look IMO

On my ASUS TUF motherboard there is simply an option in the BIOS to turn off the LEDs.

It’s an old motherboard though, bought in 2018, but I would expect the option to be available on new ones too.