Valve have released SteamOS 3.7.0 Preview, which they noted has the beginnings of support for non-Steam Deck handhelds! So we're closing in on the previously announced Beta for more handhelds. Although this release is still just for Steam Deck.
https://www.gamingonlinux.com/2025/03/steamos-3-7-0-preview-brings-the-beginnings-of-support-for-non-steam-deck-handhelds/