Ok because on my PC I had a problem, I was getting this white led when I tried to put the re size BAR in bios, I disabled the CSM module in the BIOS and every time I had this problem of led, with an update of the Vbios this has been resolved, but it does not seem to be your case here.
EDIT: however you can see if a Vbios is newer than yours here : https://www.techpowerup.com/vgabios/
Or ASUS: https://rog.asus.com/fr/graphics-cards/graphics-cards/rog-strix/rog-strix-rtx3090-o24g-gaming-model/...
I get this white light on my motherboard Dark Hero and strix 3090 OC . It happens when you boot the system up before the monitor is available. On my Asus PG35VQ if I wait for the displayport no signal light before I turn on the pc no light system boots fine. Turn the system on then monitor and white light. Deep sleep being enabled on display will cause this as well.
Cheers, it annoyed me for a short while as well. Harmless indication but really annoying if you have a glass side panel and use your pc in the dark.
Finally solved. Happy for you.