You can install SteamOS on any machine, but AMD GPU are somewhat required if you're not up to major tinkering. Valve does not officially support NVIDIA gpus atm; they are working on it.
Here's a video from Linus Tech Tips on how to do this https://www.youtube.com/watch?v=tdR-bxvQKN8 .
> Ahead of Legion Go S shipping, we will be shipping a beta of SteamOS which should improve the experience on other handhelds, and users can download and test this themselves. And of course we'll continue adding support and improving the experience with future releases.
Source: https://store.steampowered.com/news/collection/steam/?emclan...
Given NVidia's reluctance to support DRM (direct rendering manager) and Wayland, plus the general levels of nightmare that their official Linux drivers are, I wouldn't say this is Valve's fault. They've already been a poor choice on Linux 20 years ago. Even Apple has always been uneasy about their relationship (while Radeon was a less powerful choice for "premium" machines).
Also consider the ongoing AI hype. NVidia is right now very busy making their GPUs do exceptionally useful work on Linux - except the money is not in the graphics.
Interestingly, the SteamOS documentation mentions Nvidia driver support:
https://github.com/ValveSoftware/SteamOS/wiki/Getting-Starte...
That is for SteamOS 2. The newer SteamOS 3 does not officially support anything other than AMD hardware because the Steam Deck uses AMD hardware and their current focus is on improving support for that.
Not providing official support for random hardware seems reasonable. Neither do Microsoft nor Apple.