Using CUDA 11.x but getting error: Unknown CUDA arch (8.6) or GPU not supported
I'm setting up a conda environment to use pytorch 1.4.0 (on Ubuntu 20.04.2), but getting the error message:

ValueError: Unknown CUDA arch (8.6) or GPU not supported

I know this has been asked before, but no answer fits my case. This answer suggests that the CUDA version is too old. However, I updated my CUDA version to the most recent, and get the same error message.
nvcc -V says I have CUDA 11 installed, and when I run nvidia-smi I get this info:
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 460.84       Driver Version: 460.84       CUDA Version: 11.2     |
|-------------------------------+----------------------+----------------------+

which, according to the NVIDIA docs, should work be compatible:

Another auxilliary question: What does the &quot;8.6&quot; in CUDA arch (8.6) represent?

Specific versions of PyTorch work only with specific versions of CUDA.
If you are using CUDA-11.1, you'll need a fairly recent version of PyTorch. You need to either upgrade your PyTorch, or downgrade your CUDA.
