I've flown a number of DR400-180R aircraft. The ones I've flow all had a hand operated brake that applies braking equally to both mainwheels when applied. There have been no toe or heel brakes. However, when you apply rudder to turn when taxying there comes a point where the pedal you are pushing applies the brake to the mainwheel that side to assist with turning. If applying the handbrake (with the pedals central) causes a significant deviation then there is a brake problem to fix.
The other consideration is that in the air the nose wheel extends fully and disengages from the rudder controlled steering. When weight is applied to the nosewheel after the nose is lowered to the ground on landing nosewheel steering should reengage. An overinflated nose wheel olea may prevent this from happening - or a mechanical defect. Finally wear in the steering mechanism can make keeping it straight 'interesting', if there is wear it needs fixing.