Set these to 'Medium.' High-resolution shadows are barely noticeable in the heat of a race but drain GPU resources.
On Steam, select "Launch Dirt Rally 2.0 in Steam VR Mode."
NVIDIA GTX 1070 or AMD RX 580 (Minimum). For a smooth experience, an RTX 3070 or better is highly recommended.
Unlike some titles that sell VR support as a separate DLC, Dirt Rally 2.0 includes VR compatibility as part of the base game on PC. You can download it from several major storefronts:
16GB RAM is the sweet spot for loading dense track assets.