What option is selected in “Settings | Routing | Routing service”?
What option is selected in “Settings | Navigation | Rerouting mode”?
The routing is calculated in Kurviger server or via Brouter app.
Kurviger app can only use the available options provided by the selected routing services.
You need to provide a route example to understand what you mean with u-turns.
(placing waypoints on locations with u-turns, like here, then it cannot be avoided)
See also: