Not sure what you're talking about, the root password is not set, and that prevents people from being able to log into the account. Pretty standard setup on most computers nowadays where the root password isn't set on Linux.

And the entire OS is basically reaf only except for a few select folders. So for security, it's pretty solid. You can't just install a package on a steam deck, you have to use flatpack to get a package installed, or you have to install a steam game.