4K ProRes video recording is not available on 128GB iPhone 13 Pro models
Apple announced that the new iPhone 13 Pro models support 4K ProRes video recording but it is limited to 256GB, 512GB and 1TB models. The 128GB handset variant can shoot ProRes at 30fps, but at a significantly reduced resolution of 1080p.
Apple announced that the new iPhone 13 Pro models support 4K ProRes video recording but it is limited to 256GB, 512GB and 1TB models. Source: Apple Twitter