By default it uses a different UI and dedicated "window manager" (gamescope), it is not just Big Picture. But you can always switch to a traditional desktop. B

By default it uses a different UI and dedicated "window manager" (gamescope), it is not just Big Picture. But you can always switch to a traditional desktop. By far the biggest difference is that SteamOS is an immutable OS. As far as I understand, any additional package (outside of flatpacks) you install will wiped out on an OS update. So everything is fine if what you need is packaged as a flatpack, otherwise you have to hack around.