Linux

Define what you mean by non-unix like? Android is Unix like, it hides it from the user but the NDK is still a Unix like API, all devices have a POSIX shell /system/bin/sh installed which can be accessed via a terminal emulator app or using adb. The filesystem structure is different than most systems but there's still a /dev, /etc, /bin, and /proc. Not to mention one of the most unixy designs being the fork() call which android uses as the basis of all app processes. What I mean is Android has a parent process containing all the basic stuff an app needs called zygote which is then forked to become an app processes when an app is launched and then the rest of the app stuff is loaded into that new process, an exec to fully replace the parent is not done. That's a very unixy design decision that isn't usually available on other systems.

Technically speaking if we're going by the hides it from the user perspective then the steam deck qualifies to the same extent. It's hidden until a power user doesn't want it to be