Is it possible that some hardware cannot support the Ubuntu 18.04? I have the following specs in my PC, and I was told that the installation of Ubuntu 18.04 failed because the hardware doesn't support this version, but it did not give errors when Ubuntu 20.04 was installed.
The How to Install Nvidia Quadro 4000 Ubuntu 18.04 Driver tutorial that you linked to in your comment is already not up-to-date for Ubuntu 18.04, so I think it can be improved a little bit. The nvidia-driver-465 package has already been added to the default Ubuntu 18.04 repositories. To install this driver package in Ubuntu 18.04 open the terminal and type:
sudo apt update
sudo apt install nvidia-driver-465 nvidia-settings
sudo reboot
In Ubuntu 20.04 and later, run these commands instead.
sudo apt update
sudo ubuntu-drivers install
sudo reboot
The install option of ubuntu-drivers installs drivers that are appropriate for automatic installation including their dependencies.
