NVidia are the upstream for their drivers, and for a big client like Valve they would likely be willing to support the interfaces they need (and/or work with them to get them using the interfaces NVidia like). Being less coupled to the Linux kernel could go either way - yes they don't tend to support the most cutting-edge Linux features, but by the same token it's easier to get newer NVidia drivers running on old versions of Linux than it is with AMD.
(Does Valve keep the Steam Deck on a rolling/current Linux kernel? I'm honestly surprised if they do, because that seems like a lot of work and compatibility risk for minimal benefit)
> The decision to move from Debian to Arch Linux was based on the different update schedule for these distributions. Debian, geared for server configurations, has its core software update in one large release, with intermediate patches for known bugs and security fixes, while Arch uses a rolling update approach for all parts. Valve found that using Arch's rolling updates as a base would be better suited for the Steam Deck, allowing them to address issues and fixes much faster than Debian would allow. SteamOS itself is not rolling release.
Upstream is the kernel itself and standard kernel interfaces. Nvidia doing their own (non upstream) thing is the main problem here. They didn't work with libdrm for years.
Being a client or even a partner doesn't guarantee good cooperation with Nvidia (Evga has a lot to comment on that). As long as Nvidia is not a good citizen in working with upstream Linux kernel, it's just not worth investing effort in using them for someone like Valve.
Stuff like HDR support or anything the like are major examples why it all matters.
Yes, but none of that is important for a console. You're talking about integration into libraries of normal desktop distros which aren't that important when the console can just ship the compatible ones.
But Valve contributes directly to AMD drivers, they employ people working on both on Mesa and DX => vk layers. And kernel. It's very neatly integrated system.
(Does Valve keep the Steam Deck on a rolling/current Linux kernel? I'm honestly surprised if they do, because that seems like a lot of work and compatibility risk for minimal benefit)