GoG version of Batman Arkham Knight won't launch with AMD RX 7900 XT. Button greys out like it's launching for a split second then goes back to purple; trying to launch from executable doesn't work either; neither does adding -windows to a shortcut for the game.

Install the ultimate PhysX controller.

This must be installed for the game to run. Even with AMD hardware as the game requires it.

This is bloody stupid! Does anyone know where I can download it?

You can get physx from here.

https://www.nvidia.com/en-us/drivers/physx/9_18_0907/physx-9-18-0907-driver/