Unnecessary GPU consumption on 18.04 [closed]

I installed fresh ubuntu 18.04. I got two nvidia gpus on my machine. I installed nvidia drivers for them. And after installation I checked if drivers are installed properly by using nvidia-smi. And got a list of processes which are gnome-shell and xorg/Xorg. These occupy gpus unnecessarily (500MB) because I linked my monitor to iGPU. How can I get rid of these processes? :

+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|    0      1067      G   /usr/lib/xorg/Xorg                            47MiB |
|    0      1165      G   /usr/bin/gnome-shell                          51MiB |
|    0      1409      G   /usr/lib/xorg/Xorg                           191MiB |
|    0      1593      G   /usr/bin/gnome-shell                         168MiB |

Thank you in advance.

As Dorian points out in this comment The easiest most effective way that I know of to stop hardware from using resources is to remove it. (This approach has worked for over 30 years and continues to work today).

One alternative that would result in less GPU resource usage that wouldn't require removing your graphics cards would be to choose a lighter weight DE (Desktop Environment) such as LXDE or XFCE. The former is the default DE supplied with Lubuntu and the latter the default DE supplied with Xubuntu.

While it's possible to remove and add Desktop Environments at will, as the saying goes, "If it breaks, you have the pieces" and I don't recommend that course of action for anyone seeking an answer to this question.

It's far safer to backup your critical data and install a lighter version from scratch, restoring your data upon completion of installation. When changing distributions I would personally restrict what I was backing up to my personal files and scripts and just reinstall programs as needed.

If you are interested in opinions, here's a review of Linux Desktop Environments which includes pros and cons mentioned by those that expressed an opinion.