That's the whole point of GP's comment. Planes glide with the control afforded by a rudder and a vertical stabilizer. Without that, it ain't pretty.

The Lilium plane has 12 sets of 3 electric motors. Each pair of sets is powered by its own battery pack, and each set is individually actuateable. So it basically has 12 control surfaces. Separate aerodynamic controls aren't needed.

Writing control software that can handle arbitrary failures isn't easy, but there is plenty of redundancy with the three separate flight computers.

I think this “plane” has a glide ratio that’s only slightly better than a thrown rock.

Powered lift aircraft are not controllable in a glide, nor are they capable of autorotation like a helicopter. Any complete loss of power will result in an unrecoverable spin. For safety these aircraft rely on redundant systems, plus a parachute.