I followed these exact instructions and now it works:
sudo apt purge '^.*nvidia*'
sudo apt install ubuntu-desktop
sudo apt purge "^.*cublas*"
sudo apt purge "^.*cuda*"
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.old
sudo apt autoremove
sudo reboot now

While rebooting, disable Secure Boot and let then Ubuntu load completely.
sudo ubuntu-drivers devices
sudo ubuntu-drivers autoinstall
sudo reboot now

$ pip uninstall torch==1.8.0+cu111 torchvision==0.9.0+cu111 torchaudio==0.8.0 
$ pip install torch==1.8.0+cu111 torchvision==0.9.0+cu111 torchaudio==0.8.0 -f https://download.pytorch.org/whl/torch_stable.html

and now:
(fall) mona@goku:~$ python
Python 3.8.5 (default, Jan 27 2021, 15:41:15) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> torch.cuda.is_available()
True

also:
$ nvidia-smi
Mon Mar  8 13:29:44 2021       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 460.39       Driver Version: 460.39       CUDA Version: 11.2     |
|-------------------------------+----------------------+----------------------+
| 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 GTX 165...  Off  | 00000000:01:00.0 Off |                  N/A |
| N/A   42C    P8     3W /  N/A |     10MiB /  3911MiB |      0%      Default |
|                               |                      |                  N/A |
+-------------------------------+----------------------+----------------------+
                                                                               
+-----------------------------------------------------------------------------+
| Processes:                                                                  |
|  GPU   GI   CI        PID   Type   Process name                  GPU Memory |
|        ID   ID                                                   Usage      |
|=============================================================================|
|    0   N/A  N/A      1207      G   /usr/lib/xorg/Xorg                  4MiB |
|    0   N/A  N/A      1784      G   /usr/lib/xorg/Xorg                  4MiB |
+-----------------------------------------------------------------------------+

resources:
[1] Comment #12 : Bug #1871041 : Bugs : nvidia-graphics-drivers-440 package : Ubuntu
[2] Start Locally | PyTorch 1