Ah, it seems that e.g. warpAffine is provided by opencv_contrib (see e.g. https://github.com/opencv/opencv_contrib/tree/4.x/modules/cudawarping). Hmm… the only way to get the combination of arch+cuda+python+opencv+contrib seems to be to build it myself, following e.g. How to enable NVIDIA CUDA with OpenCV in Arch Linux - Jeremy's Programming Blog. Will try this now!