Lenovo might have changed its mind about releasing a SteamOS version of the soon-to-be-announced Legion Go 2. The handheld is expected to run Windows out of the box, but an official image has shown it running SteamOS. Hence, Lenovo might release the handheld in two OS versions, as it did with the Legion Go S.
I don’t think it is. Certainly is not visually different. “Game Mode” incorporates the Gamescope compositor.