@appleparan Of course I had already  checked whether CUDA is properly installed, here is the output:
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 455.28       Driver Version: 455.28       CUDA Version: 11.1     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|                               |                      |               MIG M. |
|===============================+======================+======================|
|   0  GeForce RTX 208...  Off  | 00000000:03:00.0  On |                  N/A |
|  0%   43C    P8    12W / 260W |    185MiB / 11016MiB |      1%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+`

...


@Toby Same problem with PyTorch installed with pip install torch torchvision.