You can use PyTorch on AMD. It requires quite some work (if you do not want to use the official conda build). I will be getting my new PC in 7 days which has AMD CPU. I will document the entire process to setup PyTorch on that.
PyTorch can work on ARM. I did this a long time ago. Took a rasberry pi and installed pytorch on it and it worked. I installed from a wheel that I found online (you can compile also).