What do you mean? What happens if you select one of the nVidia drivers (390, 396 or 410) and press "apply changes"?
I tried the following commands from the command line:
sudo add-apt-repository ppa:graphics-drivers
sudo apt-get purge nvidia
sudo apt-get update
First, if you want to purge a package that is updated by a PPA, you should remove it before adding the PPA, in case you believe it's packaged differently and a simple upgrade could break APT. You should either:
- add a PPA
- upgrade the packages
or, if you think that they're packaged differently:
- remove/purge the relevant packages
- add the PPA
- reinstall the packages that were removed (they will be from the PPA)
In any case, that's only if you think (from experience) that the packaging is different in the PPA. In most cases, you won't need to remove/reinstall packages, they'll be upgraded fine.
Second, there's no package named "nvidia" in the repos, you're trying to remove an inexistant package with your command #2, it did nothing. The nVidia drivers are packaged on Ubuntu in the form of nvidia-xxx, where xxx is the version of the driver: nvidia-396, nvidia-410, nvidia-390... These are the packages that would be installed from the driver manager.
So, now that you've added the graphic drivers PPA, what happens with the drivers manager and, if it doesn't work, what happens if you try to install a driver in command line, e.g.:
sudo apt-get install nvidia-410
(Replace by a different number if you want an older version.)