Percentage wise it looks small but numbers are impressive. Monthly active steam users using Linux was reported at over 1 million last year https://www.gamingonlinux.com/steam-tracker/

That will easily double in the next year with the release of the $399 Steam Deck and accompanying Proton and Steam improvements. Linux is finally about to become a serious gaming platform. (No thanks to Nvidia)

Steam deck uses AMD GPUs though, so this wouldn't help.

But the improvements Valve is making to Steam, Proton, and other areas along with game developers paying more attention to Linux compatibility will benefit all Linux users, not just Steam Deck users, and make Linux a more popular gaming platform even among people with Nvidia PCs.

Yesterday I installed Steam on my Linux machine and downloaded a random game that has no Linux port and played it. It worked perfectly, just like Windows. It was amazing.

How is that relevant to Nvidia GPU source code?

As stated upthread, "the argument is that driver source being open could help the (tiny!) Linux gaming community", and the further argument that the community will be getting larger and not only because of people using Steam Deck hardware.

I see, makes sense.

it absolutely cannot, because no official developer is going near this with a 10,000 foot pole.

https://nitter.eu/_Lyude/status/1498811646697000961