Unless there are major changes from the Deck version, I would STRONGLY advise not running SteamOS on any machine with sensitive data. You want a real login screen and, preferably, FDE for any laptop.

If you like the Desktop Mode? That is just KDE Plasma. Basically every major distro has a build that uses it (and you can install it yourself otherwise). And Steam mode is literally just Steam Big Picture (with some minor tweaks).

For a laptop? I am an old so I use Fedora. But I think everyone loves atomic distros these days so consider Bazzite.

Steam OS is basically Arch Linux with KDE and Steam that autoruns in their special mode. It would even be easier to setup for yourself.