That’s the main difference between Holo and Chimera. Their upstream setups with SteamOS are essentially the same.
Also, Nvidia drivers don’t work with any of the extra Valve tools in SteamOS (gamescope), so if you’re going the Nvidia route, I wouldn’t recommend using anything based on SteamOS anyway.
ChimeraOS is based on GNOME and immutable: https://github.com/ChimeraOS/chimeraos/wiki/OS-Comparison
That’s the main difference between Holo and Chimera. Their upstream setups with SteamOS are essentially the same.
Also, Nvidia drivers don’t work with any of the extra Valve tools in SteamOS (gamescope), so if you’re going the Nvidia route, I wouldn’t recommend using anything based on SteamOS anyway.