Mind giving a pointer? Would love to default to the mobile view, but haven't been able to find the setting you're referring to. Google hasn't helped.
Sidenote, if—like me—you actually prefer the desktop theme, and would like the opposite: to use it on mobile. There is a mobile-friendly version of it in the works, but not yet available. You can try the in-progress version on your mobile here: https://test.wikipedia.org/wiki/Main_Page?mobilaction=toggle...