There was a detail I think is important to mention and leave here, in this thread, in case someone else runs into similar issues.
When I tried to build torchvision package from source, I got the following error: ValueError: Unknown CUDA arch (3.0) or GPU not supported. The way to fix it, which I found also by searching in this forum but I can’t remember the thread, was to simply edit the file: /site-packages/torch/utils/cpp_extension.py, which is hosted in your anaconda environment, where the result of building pytorch was sent to. There you just need to find the line that contains the list:
supported_arches = ['3.5', '3.7', '5.0', '5.2', '5.3', '6.0', '6.1', '6.2',
                        '7.0', '7.2', '7.5']

… and add '3.0'. After that you can now build torchvision