According to the very authoritative work “Flugzeug Fahrwerke” (German WW2 Landing Gear) by Gunter Sengfelder the Ar 234b had no direct pilot control of nose wheel steering. It was purely a damped, free to caster nose wheel where the aircraft direction was controlled by diff braking or diff engine thrust. Although not mentioned I suspect there is a wheel centre detent or lock as suggested above.