YT performance videos show Witcher 3 running at 60FPS on Steamdeck and Arkham Knight averages around 53-55FPS on Steamdeck. Side by side comparison videos of Witcher 3 show Steamdeck has higher graphical fidelity over Switch 2 as well.
Technically, yes. WINE/Proton aren't sandboxed so it would be possible to pull some information at least. I've heard people install the flatpak version of Steam to isolate network calls using flatseal, so that's one workaround potentially.
NOTE: I'm just talking about generic data collection. The DRM/anti-cheat stuff could flag you as using Linux and then the game just refuses to run. I know the new ToS talked about banning VMs so maybe they lump linux users into that (at least for online play).
I did some more reading on this, and it apparently isn't due to DRM, its about an update to ToS that occurred in April. The update expands data collection for advertising and forced-arbitration. Arguably that's worse than kernel-level DRM. DRM can be ripped, legal shenanigans can't.
I'm assuming the post is actually about DRM operating at ring 0. That's not really root level though. That's kernel level. Root is still operating in user-mode and politely asking the kernel to interact with hardware.