It's TBD how it will handle extra buttons. I believe Valve has a kernel module for the Steam Deck controller.
Lenovo's current handheld exposes an Xbox controller and a USB device with extra buttons. Handheld Daemon synthesizes them into a virtual PlayStaton controller. If you tried to use the current SteamOS without Handheld Daemon, the 6 extra buttons wouldn't work. The community is waiting to see if Valve ships a more robust solution that Linux can standardize on, or if we'll still be using daemons like HHD for devices that don't have official Valve support.
This, the Lenovo Legion Go S—Powered by SteamOS, shares the hardware as the Windows variant, Lenovo Legion Go S. They're not building hardware specific for SteamOS yet.
I think the Orange Pi Neo is the only (other) one that's targeting Linux only. And they do have touchpads
Lenovo's current handheld exposes an Xbox controller and a USB device with extra buttons. Handheld Daemon synthesizes them into a virtual PlayStaton controller. If you tried to use the current SteamOS without Handheld Daemon, the 6 extra buttons wouldn't work. The community is waiting to see if Valve ships a more robust solution that Linux can standardize on, or if we'll still be using daemons like HHD for devices that don't have official Valve support.