Yes, SteamOS does count as Linux. Android does not. The Android and iOS Steam app is just for social features / store, not for playing games so neither show up on the survey.
SteamOS Holo, which is what the Steam Deck uses, makes up 42% of the Linux systems in the survey results.
For Skyrim I’ve had pretty good luck with just adding Vortex mod manager as a non steam game, running it with Proton and using mods that way