For the Open Source Nouveau Driver, it's included in Mesa. You may also need the xf86-video-nouveau driver for 2D acceleration on X11 depending on your hardware. For example anything older than NV50 (G80) would likely need it. Newer GPU's have seen better results when falling back onto the modesetting driver.

For the Proprietary Drivers, it depends on the distro; most allow you to install them during the installation of the distro (few do it automatically afaik), using a GUI driver manager/detection tool included in some distros or using your package manager.
A distro like fedora however requires extra steps because they're not included in the official repos.

I hope you find this more informative than "install PopOS or X distro" that includes the proprietary drivers on the installation ISO itself.

On Ubuntu it's just an option during installation. So far that's the easiest install I've seen.

OpenSUSE supports a graphical install through their software manager, but I found it caused some issues so I ended up using the command line. That was actually very easy if you're not uncomfortable using a terminal. Their docs were also accurate and easy to follow.

On fedora I followed the official docs but their instructions didn't work, so I had to find some thread on a forum with alternate instructions. It took over an hour to get it working.

For sheer ease of use I would definitely stick to Ubuntu since that's also the only distro Steam officially supports. I've had a good experience with OpenSUSE though so I'm sticking with it.