Recent changes to the SteamDB-entry of “The Stanley Parable” seem to announce an upcoming release for Linux.

about 2 hours ago Change #1177528 Changed App Config launch/2/arguments: -game thestanleyparable launch/2/config/oslist: linux launch/2/executable: stanley Changed changenumber – 1176958 › 1177528 about 6 hours ago Change #1176958 Changed oslist – windows,macos,linux Changed changenumber – 912936 › 1176958