There is a patch-series that is now merged into 6.15-rc1 that exposes more i2c/RGB controllers on the GPU side for AMD cards, so that kernel + OpenRGB (as others have mentioned) might be a solution down the line

Patch series for reference: https://lists.freedesktop.org/archives/amd-gfx/2025-January/118399.html

Yeah openrgb is your best bet, but like others already pointed out it can be hit or miss. For example i used to have a sapphire nitro+ vega 64 and that thing never worked with openrgb in linux. They used a weird implementation that someone would have to reverse engineer in order to get it working, which to my knowledge never ended up happening. At the moment i'm using a reference rx 6950xt and it just worked straight away.

Fiddle with OpenRGB and see if it works. If it doesn't, check if there's any open issues for your model of card - you might be able to aid testing, and if you're likely, someone might have already made a branch that hasn't been merged yet. That was the case with my keyboard.

Googling it, some might also have support for using hooking to the motherboard RGB header instead of internal controls.

For the iGPU issue, there should be an option in your setup utility/BIOS on your motherboard that either allows you to disable the iGPU entirely (usually in the settings for CPU or chipset, can vary from board to board), or (in the case of my Asrock board at least) there is a "dGPU only" mode that automatically disables the iGPU when a dGPU is detected. For the RGB, since the 9070XT is a partner only card (so many different manufacturers make them), the RGB implementations can vary a lot between models as there is no standard design (would be wise to edit your post to say which specific brand and model of card you have in case other people with that brand have experience with it). It might be worth just installing openRGB anyway and seeing what it detects automatically, as it could pick it up.

You can’t really disable rgb but you can set brightness with openrgb to 0. Also you could try to disable igpu in bios

Which model of the card do you have?

Which brand/model card do you have? There's no "reference design," so it matters.

Sometimes there is a small hard to see switch on some gpus that will just turn off RGB. I know asrock cards are like this.

You can take the card apart and unplug the RGB.

Downvoters: do you not own screwdrivers? Opening a video card isn't exactly hard.

Does the GPU store the RGB settings?

I use Corsair iCUE and I configure on a Windows VM. If I turn off the VM it keeps the settings in some hardware memory and works as if I configured it from Linux.