I have the Sapphire 7900XTX nitro+ and i did the following, might be the same for the 7900XT model.
It has an external A-RGB control header that you can plug into an A-RGB port on your motherboard or controller. (cable is provided)
The only caveat for linux users is that you need to use the Trixx app on Windows to change the card lighting to be controlled using an external source. This will set the control mode and persist trough reboots.